python3.odp

7/25/2019 python3.odp

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An introduction to Pythonfor absolute beginners

http://www.ucs.cam.ac.uk/docs/course-notes/unix-courses/PythonAB

Bob Dowling

ni!ersity "nformation #er!icesscientific-computing$ucs.cam.ac.uk


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But first%

&ire escapes

'o drinks or snacksin the room( please.

)oilets

'otes

#igning in&eedback


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*ourse outline + ,

ho uses Python what forhat sort of language it is

ow to launch Python

Python scripts

0eading in user data

'umbers*on!ersions*omparisons

'ames for !alues)ext

)ruth &alsehood


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*ourse outline + 1

Assignment'ames

2ur first 3real4 program

5oopsif% else%

"ndentation

*omments


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*ourse outline + 6

Lists"ndices5engths*hanging items

7xtending lists8ethods

*reating lists)esting lists

0emo!ing from lists

for% loop

"terables#lices


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*ourse outline + 9

Files0eading writing

riting our own functions

)uples

8odules#ystem modules

7xternal modules

Dictionaries

&ormatted text


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ho uses Python

2n-line games

eb ser!ices

Applications

#cience

"nstrument control

7mbedded systems

en.wikipedia.org/wiki/List_of_Python_software


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hat sort of language is Python

7xplicitly

compiledto machinecode

Purely

interpreted

*( *;;(&ortran #hell(Perl

7xplicitly

compiledto bytecode


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0unning Python + ,


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0unning Python + 1

$ python3

nix prompt

nix command

"ntroductory blurb

Python prompt

[GCC 4.6.3] on lin!"#defalt %ay 3 "&'" '()(4)4"*

Python !ersion

Python 3.".3

+++


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>uitting Python

+++ exit()

+++ quit()

+++ *trl D;

Any oneof these


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A first Python command

+++ print('Hello, world!')

,ello world-

+++

Python prompt

Python command

2utput

Python prompt


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Python commands

print

Python 3function4

(

&unction?s 3argument4

0ound brackets+ 3parentheses4

( )'Hello, world!'

3*ase sensiti!e4print PRINT


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>uotes

print *ommand

print )ext


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Alternati!e Pythons

iPython

idle


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Python scripts

hello'.py

&ile in home directory

$ python3

,ello world-

$

nix prompt

nix commandto run Python

Python script

Python script?s output

nix prompt

hello1.py

print#,ello world-*

0un from Unixprompt


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7diting Python scripts ,


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Progress

"nteracti!e Python

Python scripts

print#*command

#imple Python text


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7xercise ,

,. Print 3oodbye( cruel worldC4 from interacti!e Python.

1. 7dit e!erise'.pyto print the same text.

6. 0un the modified e!erise'.pyscript.

1 minutes

Please ask if you ha!e @uestions.


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A little more text

hello".py

print# 01 2 5*&ull 3nicode4 support

www.niode.org/harts/


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etting characters

Altr #hift; =; g

35A)"' #8A55

57))70 ") B07E74 7&''f

*haracter #elector

5inux

F


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)ext: a 3string4 of characters

+++ type('Hello, world!')

8lass str+ A string of characters

, e l l o w o r l d -'3

*lass: string

5ength: ,6

5etters

str


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)ext: 3behind the scenes4

str '3 9" '&' '&: '&: ''' 44 3" 33'&&;

&''f'6

>

#pecial 2rdinary

7n

7t

2rdinary #pecial


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7n: unwieldy for long text

AEFHB IHBLJKBM Nr. Liesey and the7nrest of these gentleOen haing asked Oe7nto write down the whole partilars7naot Ireasre sland froO the7neginning tothe end keeping nothing7nak t the

earings of the island7nand that only ease there is still7ntreasre not yet lifted take p Oy7npen in the year of grae '9__ and go7nak to the tiOe when Oyfather kept7nthe JdOiral Qenow inn and t

he rown7nold seaOan with the sare t first7ntook p his lodging nder or roof.

#ingleline


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#pecial input method for long text

Triple@uotes

rest of these gentleOen haing asked Oeto write down the whole partilarsaot Ireasre sland froO theeginning to the end keeping nothing

ak t the earings of the islandand that only ease there is stilltreasre not yet lifted take p Oypen in the year of grae '9__ and goak to the tiOe when Oy father kept

the JdOiral Qenow inn and the rownold seaOan with the sare t firsttook p his lodging nder or roof.

AEFHB IHBLJKBM Nr. Liesey and the

8ultiplelines


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Python?s 3secondary4 prompt

+++ '''Hello,world'''...

Python asking for more

of the same command.


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"t?s still Gust textC

+++ 'Hello,%nworld!'

,ello

+++

...

'''Hello,

world!'''

,ello7nworld

world7n

Python uses Hn to representline breaks in strings.

Exactlythe sameC

h i f i


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Iour choice of input @uotes:

,ello7nworld- >,ello7nworld->

>>>,elloworld->>>

,elloworld-

str '3 e l l o w o r l d -,

#ame result:

&our inputs:

P


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Progress

"nternational text

print#*

*oncatenation of strings

5ong strings

#pecial characters

7 i 1


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7xercise 1

6 minutes

,. 0eplace JJJJin e!erise".pyso it prints the followingtext Kwith the line breaksL and then run the script.

coffeeMaffeecafNcaffO

N

O 7&&e:

7&&eR

Altr

Altr

;

;

=

e

e

Att hi t l


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Attaching names to !alues

Oessage S ,ello world-print#Oessage*

hello3.py

str '3 e l l o w o r l d -,Oessage

3!ariables4

+++ e**+-e'Hello, world!'

+++ e**+-e

,ello world-

+++ type(e**+-e)

8lass str+

Att hi t l


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Attaching names to !alues

Oessage S ,ello world-print#Oessage*

hello4.py

print function

str '3 e l l o w o r l d -,Oessage

+++ type(print)

8lass iltin_fntion_or_Oethod+

0 di t t i t i t


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0eading some text into a script

$ python3

MesT

input1.py

Qoo-

/oo!

Oessage S inpt#MesT*

print#Oessage*

inpt'.py

inpt#MesT*

Oessage S ;

print#Oessage*

*anQt read numbers directlyC


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*anQt read numbers directlyC

nOer S inpt#T*

print#nOer = '*

inpt".py

$ python3 input.py

T 1&

Iraeak #Oost reent all last*) ?ile >inpt".py> line " in 8Oodle+

print# = *

string integer

nOer

IypeBrror)Cant onert int oUetto str iOpliitly

'

inpt#*: strings only


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inpt#*: strings only

nOer S inpt#T*

print#nOer = '*

inpt".py

$ python3 input.py

T 1&

inpt#T * str " &'

int '&R

#ome more types


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#ome more types

+++ type('Hello, world!')

8lass str+

+++ type(0)

8lass int+

+++ type(3.1012)

8lass float+

string of characters

integer

floating point number

*on!erting text to integers


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*on!erting text to integers

+++ int('1&')

'&

+++ int('1&&')

V'&&

+++ int('1&&1&')

WaleBrror)inalid literal for int#* with ase '&) '&&V'&

str " &' int '&

str 6 V

int V'&&

&' &

*on!erting text to floats


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*on!erting text to floats

+++ lo+t('1&.&')

'&.&

+++ lo+t('1&.')

'&.&

Q,S.SQ is a string

,S.S is a floatingpoint number

*on!erting between ints and floats


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*on!erting between ints and floats

+++ lo+t(1&)

'&.&

+++ int(1&.2)

'& )runcatesfractional part

+++ int(1&.2)

V'&

*on!erting into text


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*on!erting into text

+++ *tr(1&)

'&

+++ *tr(1&.&&&)

'&.&

integer

float

string

string

*on!erting between types


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*on!erting between types

int#*

float#*

anything

anything

integer

float

str#* anything string

&unctions named after the type they con!ert into.

0eading numbers into a script


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0eading numbers into a script

te!t S inpt#T *

nOer S int#te!t*print#nOer = '*$

T

''

python3 input3.py

1&

#tepping through our script ,


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#tepping through our script ,

te!t S inpt#T*

nOer S int#te!t*print#nOer = '*

str 3 T

#tepping through our script 1


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te!t S inpt#T*


str 3 T

inpt function

str " &' 'B: text( not number



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te!t Sinpt#T *


inpt function

str " &'te!t



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te!t S inpt#T *


inpt function

str " &'te!t

int function

int '&

#tepping through our script T


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#tepping through our script T

te!t S inpt#T *


inpt function

str " &'te!t

int function

int '&nOer

#tepping through our script U


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te!t S inpt#T *

nOer Sint#te!t*print#nOer = '*

int '&nOer

#tepping through our script V


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#tepp g t oug ou sc pt

te!t S inpt#T *


int '&nOer

function

int ''

=

int '



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pp g g p

te!t S inpt#T *


int '&nOer

int ''

functionprint

Progress


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g

'ames

)ypes

)ype con!ersions

Ealues

0eading in text

str#* int#* float#*

inpt#prompt*

nameS value

strings

integers

floating point numbers

7xercise 6


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0eplace the two JJJJin exercise6.pyto do the following:

,. Prompt the user with the text 3ow much4.

1. *on!ert the user?s answer to a floating point number.

6. Print 1.T plus that number.

6 minutes

"ntegers


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g

W% -1( -,( S(,( 1( 6( 9 %X

"nteger addition subtraction


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g

+++ &

"(

+++ &

'(

#paces around theoperator don?t matter.

3'o surprises4

"nteger multiplication


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)here is no 3Y4 on the keyboard. 5inux:(;#hiftAltr ;

se 3X4 instead

+++ &4

'&&

#till no surprises

"nteger di!ision


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)here is no 3Z4 on the keyboard. 5inux:.;#hiftAltr ;

se 3/4 instead

+++ &5

4.& )his is a floating point numberC

#urpriseC

"nteger di!ision gi!es floats C

C


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&ractions

+++ &50&

&.(

+++ &53&

&.6666666666666666

&loats sometimes

*onsistency &loats always

C

"nteger di!ision gi!es floats C

C


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+++ &550

(

C// #pecial operation to stick with integers

+++ 1550

(+++ 1550

V6

+++ &50

(.&

+++ 150

(."(+++ 150

V(."(

"nteger powers


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)here is no 3914 on the keyboard.

se 3XX4 instead

+++ 044

'6

+++ 044

Aynta!Brror) inalid synta!

#paces aroundtheoperator don?t matter.

#paces inthe

operator doC

"nteger remainders


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e.g. "s a number e!en or odd

+++ 06

&

+++ 6

'

se 3Y4

+++ 6

' 0emainder is always non-negati!e

ow big can a Python integer be


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+++ 44

4

+++ 044'6

+++ 1744"(6

+++ 7446((36

+++ 73744

4"R4R69"R6

+++ 7446((36

+++ 7446((36

+++ 44

4



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+++ 02027#2744

':446944&939&R(('6'6

+++ 1"007#00#&2171744

34&":"366R"&R3:4634633946&943'96:"''4(6

+++ 30&"3772&23"0730733#07#7"110744''(9R"&:R"393'6'R(4"3(9&R:(&&:6:9R&9:(3"6RR:466(64&(64&3R4(9(:4&&9R'3'"R63RR36

+++ 11#2&"23#3171203#&2"&&"7"#2"372

'34&9:&9R"RR4"(R9&RR(94&"4RR:"&(:46'"949R36(:"&(R"3R33999"3(6'4439"'964&3&&93(46R96:&':94"R:'66R&34"96R&&3':(:':64:6&(&:(39(3::":''R46(6RR4643364R&&6&:4&R6

2"07770&70&320#"0&



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,S996[[[[,9,6,T1TSUU\,VT1V,SV,UU196[1TV\\U919\S9V6[6V[S6[91669[61[6\T6\SV\V,TTV9TU[9[[1U[,,\69\\VTT[69S[\S,SUV,996\1U1[6V\[VTV696[,[TV\6USV1U616US[V[T,6UT1VV\9T\TU\VUT96VS\\\[69S6U,T\S,696[6V,[6,991[SVSS,,[TT\9U11U6VU6,[[6\6\VV,1V9TUV1669U[9699T[UU,V9\U[SV\S[VST[S6VS9SV,1[9S9[V9S,,[US\,,99UV\VVV[6T\[S1\SSUU[U\6[\VU[[,V[VV[T\9U\STU6S,\S1US\9ST\\TV\9T6961[169U\6S6S1UU\U996ST\S1TS,T\V16\\[UVV,91,TT9,U\6[6TTT\[[T1\,9[U6,[16V\,99699\UV69S[V[,,[V1U6\9\U9VT,SS,[\S9,69\SS[9,VSU,U

VTS\6UU[666[TSTT,S61\V1S[[1U\TTSVU\\[6U,U6U\9,,\66S,T1,6V\U[1T[6V,[[S\,[66UTUVT,11,6,[9\1[9U6U[,1TTTS11T\\[6SS9,1699V[9[U1T\TUV99\1,\9U,VS16[SUTST\,619TU,S[1TV6,[6T6[SS[VUS[U11,S1[691VS,\VU\[1S16,6,U\S,VUV[SSUUVT,\T9[TSV\\1,U6U9,\6VS1[T6VT,19V[9S,9\SV,T\,6T9T\\[1V\ST,66\\U,,TT,V\91V,,SU[6,,69S\ST[91V1[[91V\V\,TT9[9\V[1\T9616T69T,VSUT1161U\SU,6\9\ST\[VU\6SS1,11\U66\TU[VV[1[V[\9[99SU,USSV9,1\9TUV9\,\[16STSTV,U916VV,T9[,U61,6[SU6,S9T\S1\,U,6U\1UVS[691[TU99SV6S99V[\\\V,\S,V[,

9UTVU69V6116[TS1UV1T6ST\[\\V\T\\US\SV\\9U\1S,VV9U19[,VV,[99\[UV9TTUT\1TS,V[61\SVS9V6,,\966,UTTTS[SVTU[11,[9UTV,V9U6V61\U[[9\,1[,\T1S6,V9TVSS199S\1UU,U\,S[V9,9[6[TSV[9,,\1\[S9T11\[,[TV66[\VVU9[,S6,1US[T\S6SS,6S19,69UV,[\V1UUV61,U9\,T,,,6,US1\1SV[,V6[S6696US\S196[S9VS[69S9S6,T9,\S66U

)here is no limitC

7xcept formachinememory

Big integers


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1

9

,U

1TU

UTT6U

91\9\UV1\U

,[99UV99SV6VS\TT,U,U

69S1[16UU\1S\6[9U69%U66V9USV96,VU[1,,9TU

* / *;;&ortran

2ut of the reachof * or &ortranC

long long"')770],U

long"')770][

int

"')770]9

&loating point numbers


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,.S

S.66666666

6.,9,T\1UT1.V,[1[,[1

Basic operations


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+++ &.& .&"(.&

+++ &.& .&'(.&

+++ &.& 4 .&

'&&.&

+++ &.& 5 .&

4.&

+++ &.& 44 .&

3"&&&&&.&

7@ui!alent to integer arithmetic

&loating point imprecision


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+++ 1.& 5 3.&&.3333333333333333

+++ 1&.& 5 3.&

3.333333333333333(

^ 17significant figures

"f you are relying onthis last decimal place(you are doing it wrongC

idden imprecisionC


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+++ &.1&.'

+++ &.1 &.1

&."

+++ &.1 &.1 &.1

&.3&&&&&&&&&&&&&&&40eally: if you are relying onthis last decimal place(you are doing it wrongC

C

ow big can a Python float be + ,


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+++ 737.&444"R4R69"R6.&

+++ 02027#27.&44

'.:446944&939&R(("e='R

#o far( so good.

#witch to

3scientific notation4

,.[99UV99SV6VS\TT1

,.[99UV99SV6VS\TT1

Y,S,\

e;,\

&loats are not exact


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+++ 02027#2744

':446944&939&R(('6'6

+++ 02027#27.&44'.:446944&939&R(("e='R

"nteger

&loating point

,.[99UV99SV6VS\TT1Y,S,\ ,[99UV99SV6VS\TT1SSS

,[99UV99SV6VS\TT,U,U-

6[9

ow big can a Python float be + 1


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+++ 1."007#00#&2e12443.4&":"366R"&R3:(e=3:

+++ 3.0&"3772&23"e3"44

'.'(9R"&:R"393'6"e=99

+++ 1.1#2&"23#317e##44

'.34&9:&9R"RR4"(R9e='(4

+++ 1.30"#e1044

DerflowBrror) #34Oerial reslt ot of range*

#o far( so good.

)oo bigC

&loating point limits


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'."34(69:R&'"34(69Z'&

,V significant figures

-61T _ ' _ 6S[

9.\9SUTU9T[9,Y,S-619_ ' _ [.\[[9UTUV96,Y,S6SV

Positi!e !alues:

*omplex numbers


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z

z2

+++ (1.&.8)44

#'.3'"(='."(U*

Progress


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Arithmetic

"ntegers


*omplex numbers

= V X / XX Y

'o limitsC

5imited si`e

5imited precision

7xercise 9


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6 minutes

0eplace the JJJJin e!erise4.pyto e!aluateand print out the following calculations:

,. 116 Z V,

1. K, ; ,/,SSL,SS

6. K, ; ,/,SSSSL,SSSS

9. K, ; ,/,SSSSSSL,SSSSSS

'ote: Brackets work inPython arithmetic Gust like theydo in normal mathematics.

*omparisons


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T _ ,S

T ,S

*omparisons


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+++ 9 1&

Ire

+++ : 1&

?alse

Asking the @uestion

Asking the @uestion

)rue &alse


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+++ type(True)8lass ool+ 3Booleans4

T ,S;

T ,S_

int int

,T

)rue

int

bool

)rue &alse


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bool

bool

Ire

?alse

2nly two !alues

#ix comparisons


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8aths

=

Python

SS

-S

8

+

8S

+S

Doublee@uals sign

7@uality comparison assignment


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naOeS ale

S

ale'SS ale

"

SS

Attach a name to a !alue.

*ompare two !alues

)extual comparisons


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+++ '+t' 9 'do-'

Ire

Alphabetic ordering

+++ ';+t' 9 '+t'

Ire

+++ '


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erman:

#wedish:

` _

_ `

Python ine@ualities use nicode character numbers.

)his is o!er-simplistic for 3real4 use.

Alphabetical order

3*ollation4 is a whole field of computing in itself

3#yntactic sugar4


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& 8 nOer 8 '&

& 8 nOer

and

nOer 8 '&

+++ nu=er

+++ & 9 nu=er 9 1&

Ire

*on!erting to booleans


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float#* *on!erts to floating point numbers

int#* *on!erts to integers

str#* *on!erts to strings

=ool#* *on!erts to booleans

8lass float+

8lass int+

8lass str+

8lass ool+

seful con!ersions


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?red Ire

?alse

'on-empty string

7mpty string

' Ire

& ?alse

'on-`ero

ero

'" Ire

V' Ire

Boolean operations


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'umbers ha!e ;( ( ]%

hat do booleans ha!e

bool

bool

bool

bool

bool

Boolean operations + 3and4


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bool

bool

booland

Ire Ireand

Ire ?alseand

?alse Ireand

?alse ?alseand

Ire

?alse

?alse

?alse

Both ha!eto be )rue

Boolean operations + 3and4


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+++ 0 9 +nd 7 9 #

Ire

4 8 (

6 8 9

Ire

Ire

and Ire

+++ 0 9 +nd 7 : #

?alse

4 8 (

6 + 9

Ire

?alseand ?alse

Boolean operations + 3or4

b l


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bool

bool

boolor

Ire Ireor

Ire ?alse

?alse Ire

?alse ?alse

Ire

?alse

Ire

Ire

At leastone hasto be )rueor

or

or

Boolean operations + 3or4


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+++ 0 9 or 7 9 #

Ire

4 8 (

6 8 9

Ire

Ire

or Ire

+++ 0 9 or 7 : #

Ire

4 8 (

6 + 9

Ire

?alse or Ire

Boolean operations + 3not4


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bool boolnot

Irenot

?alse Ire

?alse

not

Boolean operations + 3not4


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+++ not 7 9 #

?alse

6 8 9 Ire not ?alse

+++ not 7 : #

Ire

6 + 9 ?alse not Ire

Ambiguity in expressions


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6 ; U / 6

K6 ; UL / 6 6 ; KU / 6L

6 T

Di!ision before addition


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T

6 U / 6;

6 1;

Di!ision first

Addition second

32rder of precedence4


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!44y !4y!5y!6y !y!y!!

!y !:y!:y!!y !9y!9y

not! ! or y! +nd y

&irst

5ast

Progress

*omparisons SS -S 8 + 8S +S


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*omparisons - 8 + 8 +

Booleans Ire ?alse

'umerical comparison

Alphabetical ordering

( 8 9

dig 8 dg

Boolean operators and or not

*on!ersions &

&.&

?alse

?alse

?alse

other Ire

7xercise T

Predict whether these expressions will e!aluate to Ire or ?alse


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6 minutes

Predict whether these expressions will e!aluate to Ireor ?alse.)hen try them.

dog + Cat or 4( Y 3 SS &

sparrow + eagle

6& V 4( / ( = '& SS '

,.

1.

6.

'ames and !alues: 3assignment4


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+++ +lph+ 1&&

,.+lph+ 1&&

1. +lph+ 1&&

int '&& Python createsan 3integer ,SS4in memory.

int '&&alpha

Python attachesthe name 3alpha4to the !alue.

Assignment: right to left


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+lph+ 1&&

30#4: right hand side

7!aluated first

35#4: left hand sideProcessed second

#imple e!aluations

+++ =et+ 1&& &


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+++ =et+ 1&& &

0#,. 1&& &

int '&& function = int "&

int '"&1.

int '"&6. eta

5#

*hanging !alue ,

+++ -++ 1


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-++ 1

+++ -++

*hanging !alue 1

+++ -++ 1

0#


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-int '

*hanging !alue 6

+++ -++ 1

5#


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-

int 'gaOOa

*hanging !alue 9

+++ -++ 1

0#


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-

+++ -++ int 'gaOOa

int "

*hanging !alue T

+++ -++ 1

5#


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-

+++ -++ int 'gaOOa

int "

*hanging !alue U

+++ -++ 1

garbage collection


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+++ -++ int 'gaOOa

int "

*hanging !alue V

+++ -++ 1


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+++ -++ gaOOa

int "

*hanging !alue a subtlety

+++ -++ 1


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+++ -++ gaOOa

int "

int '

)wo separate

integer obGects.

Python doesn?t change an integer?s !aluePython replacesthe integer.

Python integers are 3immutable4

'ames on the 0# ,

+++ delt+ +lph+ 0&


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0#,.

+lph+ 0&

function = int 4&int '&&

alpha

int '4&

1.

6.

'ames on the 0# 1

+++ delt+ +lph+ 0&


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5#9. delta int '4&

#ame name on both sides S


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delta int '4& #tartingposition

+++ print(delt+)

'4&

#ame name on both sides ,

+++ delt+ delt+ 1&0#


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,. delt+ 1&

function = int '&int '4&

delta

int '(&

1.

6.

9.

#ame name on both sides 1



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T.

U.

int '(&

int '4&delta

0#

int '(&

int '4&delta

0#

#ame name on both sides 6



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V.

[. int '(&delta

int '(&

int '4&delta 'o longer

used.

3#yntactic sugar4

thing =S '& thing S thing = '&


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thing =S '& thing S thing ='&

thing VS '& thing S thing V'&

thing XS '& thing S thing X'&

thing /S '& thing S thing /'&

thing XXS '& thing S thing XX'&

thing YS '& thing S thing Y'&

is e@ui!alent to

Deleting a name + ,

+++ print(thin-)


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+++ print(thin-)

Iraeak #Oost reent all last*) ?ile >8stdin+> line ' in 8Oodle+

+++ thin- 1

+++ print(thin-)

'

aOeBrror) naOe thing is not defined

nknown!ariable

Deleting a name + 1

+++ print(thin-)


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+++ print(thin-)


+++ del thin-

+++ print(thin-)

'

aOeBrror) naOe thing is not defined

nknown!ariable

Mnown!ariable

Progress


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Assignment

#trictly right to left

; etc. 3syntactic sugar4

thing S thing = '&

thing S thing = '&

1nd ,st

thing =S '&

Deletion del thing

2ur first 3real4 program

$ python3 *qrt py e ha!e to write srt py


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'.4'4"'3(6"393&R(

$OerTpython3 *qrt.py

.&e ha!e to write srt.py

&irst( the maths.)hen( the Python.

#@uare root of 1.Sby 3bisection4

S S too small for 1


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3"nter!al of uncertainty4

S.S too small for 1

1.S too large for 1

S.S _ 1 _ 1.S

#@uare root of 1.Sby bisection ,

#& & = " &* / " &


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8id-point: ,.S

#&.&= ".&* / ".&

'.&

'.&XX"

'.&

#@uare root of 1.Sby bisection 1

midpoint 2

11

_


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'.&XX" 8 ".&

,.S _ 1 _ 1.S

so change lowerbound

midpoint 2_


#'.& = ".&* / ".&


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8id-point: ,.T

#'.&= ".&* / ".&

'.(

'.(XX"

"."(


'.(XX" + ".&


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'.( " ".&

so change upperbound

,.S _ 1 _ ,.T

#@uare root of 1.Sby bisection T

#'.& = '.(* / ".&


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8id-point: ,.1T

#'.& '.(* / ".&

'."(

'."(XX"

'.(6"(

#@uare root of 1.Sby bisection U

'."(XX" 8 ".&


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,.1T _ 1 _ ,.T

#@uare root of 1.Sby bisection V

#'."(= '.(* / ".&


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8id-point: ,.6VT

# *

'.39(

'.39(XX"

'.:R&6"(

#@uare root of 1.Sby bisection [

'.39(XX" 8 ".&


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,.6VT _ 1 _ ,.T

7xercise U

One more iteration.


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,.6VT _ 1 _ ,.T

&ind the mid-point.#@uare it.

*ompare the s@uare to 1.S.

Do you chane thelower or upper bound

1 minutes

nderstanding before Programming


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And now using PythonC

lower S &.&pper S " &


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pper S ".&

Oiddle S #lower=pper*/"

And now using Python 1

OiddleXX" 8 ".&


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Ire

lowerS Oiddle

print#lower pper*

".&'.&



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print# OiddleXX"*Oiddle

"."('.(


OiddleXX" 8 ".&


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?alse

pperS Oiddle

print#lower pper*

'.('.&

And now using Python T


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'.(6"('."(

And now using Python U

OiddleXX" 8 ".&


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Ire

lowerS Oiddle

print#lower pper*

'.('."(

And now using Python V


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'.:R&6"('.39(

And now using Python [

OiddleXX" 8 ".&


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Ire

lowerS Oiddle

print#lower pper*

'.('.39(

5ooking at the Python codelower S &.&pper S ".&


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print#Oiddle OiddleXX"*

OiddleXX" 8 ".&

lower S Oiddle pper S Oiddle

print#lower pper*

5ooking at the Python structureslower S &.&pper S ".&

#et up

5oop


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print#Oiddle OiddleXX"*

OiddleXX" 8 ".&


print#lower pper*

*hoice

5ooping

Before


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5oop test

5oop body

After

#hould theloop run

KagainL

hat isrun eachloop

5oop example: *ount from , to ,S

nOer S 'Before


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nOer 8S '&

print#nOer*nOer =S '

print#None-*

5oop test

5oop body

After


nOer S 'nOer S '


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nOer 8S '&


print#None-*

while


print#None-*

)nOer 8S '&

5oop test: *ount from , to ,S

nOer S '

3while4 keyword

l t t


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while

print#None-*

)nOer 8S '&

loop test

colon


5oop body: *ount from , to ,S

nOer S '


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while

print#None-*

)nOer 8S '&

loop body

indentation


nOer S '

while nOer 8S '& )


$

'"

python3 while1.py


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print#nOer* nOer =S '

print#None-*

while'.py

34(

69:R'&

None-$

Python?s use of indentation

nOer S '


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while nOer 8S '& )

p


&our spaces? indentationindicate a 3block4 of code.

)he block formsthe repeated lines.

)he first unindented linemarks the end of the block.

rint#None-*

c.f.3legalese4

,,KaL


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,KaL

,KbL,KbLKiL

,KbLKiiL

,KbLKiiiL

,KcL1

6

2ther languages

#hell while ...

do...

do ... done #yntax


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*

...done

while ...\......

\ ... #yntax

...

...

*larity

*larity

Progress

while ... ) efore

whiletest)ti


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action1

action2

action3

afterwards

test to keep looping

code blocks

indentation

7xercise V

&or each script:

Predict what it will do

while".py

while3 py


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T minutes

Predict what it will do.

0un the script.

ere you right

while3.py

while4.py

while(.py

)o kill a running script: *trl *;

while6.py

Back to our s@uare root example

S.S 1.S

1.S

uncertainty

,.SY,S,T

tolerance


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,.T,.6VT

,.S 1.S

,.S

,.S ,.T

S.T

,.1T ,.T

S.1T

S.,1T

Y

Y

Y

Y

hat we get

hat we want

Meep looping while % toleranceuncertainty


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while nertainty + tolerane )

Do stuff.

#@uare root: the loop

lower S &.&

pper S ".&

tolerane S '.&eV'(

nertainty S pper V lower

#et up

5


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Oiddle S #lower = pper*/"


print#lower pper*

5oop

*hoice

*hoosing

OiddleXX" 8 ".&

*hoice


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OiddleXX" 8 ".& Ire ?alseor

Ire

?alse

lower S Oiddle

pper S Oiddle

#imple example

te!t S inpt#OerT *nOer S int#te!t*

if nOer Y " SS &) print#Ben nOer*

$

OerTBen nOerIhat was fn

python3 ithenel*e1.py

"


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p # *else) print#Ddd nOer*

print#Ihat was fn-*

ifthenelse'.py

Ihat was fn

$

OerTDdd nOerIhat was fn

python3 ithenel*e1.py

#

if%then% else% + ,

if )nOer Y " SS &

ifkeyword

)est

*olon


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if

else )

print#Ben nOer*

pper S Oiddle

)nOer Y " & *olon

print#Ihat was fn-*

if%then% else% + 1

if )nOer Y " SS &


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if

else )

print#Ben nOer*

pper S Oiddle

)nOer Y " &

0un if test is "rue

"ndentation

print#Ihat was fn-*

if%then% else% + 6

if )nOer Y " SS &


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else )

print#Ben nOer*

pper S Oiddle

else)keyword

0un if test is False

"ndentationprint#Ihat was fn-*

if%then% else% + 9

if )nOer Y " SS &


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else )

print#Ben nOer*

pper S Oiddle

0un afterwardsregardlessof testprint#Ihat was fn-*

2ur s@uare root example


if

Before

)OiddleXX" 8 ".&


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else )

print#lower pper*

lower S Oiddle

pper S Oiddle

After

if% block

Progress

if ... ) efore

iftest)action

1

else)


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1

action2

else)action

3

afterwards

choice of two

code blocks

indentation

7xercise [

&or each script:

Predict what it will do.

ifthenelse".py

ifthenelse3.py


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T minutes

0un the script.

ere you right

ifthenelse4.py

Back to our example

lower S &.&

pper S ".&

tolerane S '.&eV'(



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print#lower pper*

if OiddleXX" 8 ".& )

else )

pper S Oiddle

lower S Oiddle

Doublyindented

ifstartsindented

5e!els of indentation

lower S &.&

pper S ".&

tolerane S '.&eV'(



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print#lower pper*

if OiddleXX" 8 ".& )

else )

pper S Oiddle

lower S Oiddle

9 spaces

[ spaces

)rying it out

tolerane S '.&eV'(lower S &.&

pper S ".&nertainty S pper V lower


$

'.& ".&'.& '.('."( '.(3

python3 *qrt1.py


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while nertainty + tolerane ) Oiddle S #lower = pper*/"

if OiddleXX" 8 ".&) lower S Oiddle else) pper S Oiddle

print#lower pper*


srt'.py

'.39( '.('.39( '.439(

'.4&6"( '.439('.4&6"( '.4"':9(

...

'.4'4"'3... '.4'4"'3...

#cript for the s@uare root of ".&

lower S &.&

tolerane S '.&eV'(


hil t i t t l

pper S .& 1.S


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print#lower pper*

if OiddleXX" 8 .&)

else )

pper S Oiddle

lower S Oiddle

1.S

"nput target

te!t S inpt#OerT *nOerS float#te!t*


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if OiddleXX" 8 nu=er)

%

"nitial bounds

lower S >pper S >


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# ,.S ,.S _ $#_ #

,.S # ,.S $# #

if...then...else...

"nitial bounds

if nOer 8 '.& )lower S nOerpper S '.&else )


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else )lower S '.&pper S nOer

eneric s@uare root scriptte!t S inpt#OerT*nOer S float#te!t*

if nOer 8 '.&)

lower S nOerpper S '.&else)lower S '.&

ser input

"nitiali`ation


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pper S nOer

tolerane S '.&eV'(


while nertainty + tolerane)Oiddle S #lower=pper*/".&if OiddleXX" 8 nOer)lower S Oiddleelse)

pper S Oiddle


print#lower pper*

Processing

2utput srt".py

'egati!e numbers

'eed to catch negati!e numbers


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e!it#*

if nOer 8 &.&)print#Oer Ost e positie-*

>uit immediately

else is optional

3*hained4 tests

te!t S inpt#OerT*

nOer S float#te!t*


ser input

"nput !alidation


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e!it#*

if nOer 8 '.&)lower S nOerpper S '.&else)lower S '.&pper S nOer

...

"nitiali`ation

3*hained4 tests + syntactic sugar

te!t S inpt#OerT*

nOer S float#te!t*


i #*


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elif

e!it#*

nOer 8 '.&)lower S nOerpper S '.&else)lower S '.&pper S nOer

...

elif: 3else if4

srt3.py

ithout elif%

te!t S inpt#OerT*

nOer S float#te!t*

if nOer 8 &.&)print#Oer is negatie.*l


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else)if nOer 8 '.&)print#Oer is etween ^ero and one.*else)if nOer 8 ".&)print#Oer is etween one and two.*else)if nOer 8 3.&)print#Oer is etween two and three.*else)print#Oer is three or Oore.*

#tacked clauses get unwieldy

ith elif%

te!t S inpt#OerT*

nOer S float#te!t*

if nOer 8 &.&)print#Oer is negatie.*lif 8 ' &


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elif nOer 8 '.&)print#Oer is etween ^ero and one.*elif nOer 8 ".&)print#Oer is etween one and two.*elif nOer 8 3.&)print#Oer is etween two and three.*else)print#Oer is three or Oore.*

Progress

'ested structures

if% )

while % ) if % )

*hained tests


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%elif% ) %elif% ) %else)

%

)esting inputs to scripts

e!it#*

7xercise \

e!eriseR.py

,. 7dit the s@uare root script to catch negati!e numbers.

Only attempt each part afteryou ha%e the pre%ious part wor&in!


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,S minutes

@ p g

1. 7dit the s@uare root script to ask for the tolerance.

6. 7dit the s@uare root script to catch negati!e tolerances.

*omments

e ha!e written our first real Python script

hat did it do


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Whydid it do it

'eed to annotate the script

Python comment character

)he 3hash4 character

=a.k.a. 3pound4( 3number4( 3sharp4


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5ines starting with 3=4 are ignored

Partial lines starting 3=4 are ignored

sed for annotating scripts

=

Python commenting example

Aript to allate sare roots y isetion #* Qo Nowling "&'". Liensed nder GPL 3.&te!t S inpt#OerT*nOer S float#te!t* eed a real nOer

Iest nOer for alidity


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Iest nOer for alidity set initial onds if D`.if nOer 8 &.&)print#Oer Ost e nonVnegatie-*e!it#*elif nOer 8 '.&)lower S nOerpper S '.&else)lower S '.&pper S nOer

2n a realnix system%

-/sr/in/python3

Aript to allate sare roots y isetion #* Qo Nowling "&'". Liensed nder GPL 3.&te!t S inpt#OerT*nOer S float#te!t* eed a real nOer


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nOer float#te!t* eed a real nOer

8agic line for executable files

$

instead of

u=+r.py

$ python3 u=+r.py

Progress

*omments =


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=3=4 character


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hole numbers


-,1V

6.,9,T\1UT6T[\V\6


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)ext

Booleans

Ihe at sat on the Oat.

)rue &alse

*omplex numbers K,.S ; 1.SGL

5ists

[ hydrogen heliO lithiO erylliO

oron ; thoriO protatiniO raniO]


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[ V3.'4'(R"6(3(:R9R3 V'.(9&9R63"69R4:R66

&.& '.(9&9R63"69R4:R66 3.'4'(R"6(3(:R9R3]

[ " 3 ( 9 '' '3 '9 'R]

hat is a list

A sequenceof !alues )he names of the elements

hydroen' helium' lithium' beryllium' (' protactinium' uranium


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"ndi!idual !alue identifiedby position in the se@uence

3helium4 is the name of thesecond element

Ealues stored in order Atomic number order

hat is a list

A sequenceof !alues )he prime numbersless than sixty

)' *' +' 7' 11' 1*' 17' 1,' )*' ),' *1' *7' -1' -*' -7' +*' +,


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"ndi!idual !alue identifiedby position in the se@uence

less than sixty

V is the fourth prime

Ealues stored in order 'umerical order

*reating a list in Python

+++ prie* ? , 3, , #, 11, 13, 1#, 12@

i

A literal list


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+++ prie*

[" 3 ( 9 '' '3 '9 'R]

+++ type(prie*)

8lass list+

)he whole list

A Python type

ow Python presents lists

#@uare brackets

at the ends


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[ ]'R'9'3''9(3 "

*ommas between items

#@uare brackets

priOes S [" 3 ( 9 '']5iteral list


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Python counts from ero

96(43"'&3index4


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[ ]'R'9'3''9(3 "3!alue4

5ooking things up in a list

+++ prie* ? , 3, , #, 11, 13, 1#, 12@

[ ]'R'9'3''9(3 "

96(43"'&


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[ ]'R'9'3''9(3 "

+++ prie*

"

+++

'9

@&?

index

prie* @7?

s@uare brackets

#@uare brackets

priOes S [" 3 ( 9 ''] 5iteral list

priOes[3] "ndex into list


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*ounting from the end

+++ prie* ? , 3, , #, 11, 13, 1#, 12@

[ ]'R'9'3''9(3 "

96(43"'&


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[ ]'R'9'3''9(3 "

+++

'R

prie* @1?

getting at the last item

V'V"V3V4V(V6V9V:

"nside !iew of a listlist

:

priOesint 3

int " primesjS

primesj,


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int 'R

%

priOes

int '9 primesjU

primesjV

5ength of a list

priOes

list

:

+++ len:

(prie*)

S len#*function:length of list


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priOes

V8aximumindex is V

*hanging a !alue in a list

+++ d+t+ ?'+lph+', '=et+', '-++'@

+++ d+t+?@

gaOOa

d ? @ ' '

)he list

"nitial !alue


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+++ d+t+?@ 'A'

+++ d+t+?@

G

+++ d+t+

[alpha eta G]

*hange !alue

*heck change

*hanged list

*hanging a !alue in a list + ,

+++ d+t+ ?'+lph+', '=et+', '-++'@

list

3 str ( a l p h a

0ight to left


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str 4 e t a

str ( g a O O a

*hanging a !alue in a list + 1

+++ d+t+ ?'+lph+', '=et+', '-++'@

data

list

3 str ( a l p h a

0ight to left


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data

str 4 e t a

str ( g a O O a


+++ d+t+?@ 'A'

0ight to left

data

list

3 str ( a l p h a


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data

str 4 e t a

str ( g a O O a

str ' G 'ew !alue


+++ d+t+?@ 'A'

0ight to left

data

list

3 str ( a l p h a


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data

str 4 e t a

str ( g a O O a

str ' G'o longerreferenced

*hanging a !alue in a list + T

+++ d+t+?@ 'A'

0ight to left

data

list

3 str ( a l p h a


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data

str 4 e t a

str ' G

0emo!ing an entry from a list + ,

+++ del d+t+?1@

data

list

3 str ( a l p h a data[&]


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data

str 4 e t a

str ( g a O O a

data[']

data["]

0emo!ing an entry from a list + 1

+++ del d+t+?1@

data

list

" str ( a l p h a data[&]


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data

str 4 e t a

str ( g a O O a data[']

'o longerreferenced

0emo!ing an entry from a list + 6

+++ del d+t+?1@

data

list

" str ( a l p h a data[&]


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str ( g a O O a data[']

0unning off the endlist

:

priOesint 3

int "


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int 'R

%

int '9

primesj[

0unning off the end

+++ len(prie*)

:

+++ prie*?#@

'R


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'R

+++ prie*?"@


nde!Brror) list inde! ot of range

)ype of error Description of error

0unning off the end

+++ prie*?"@ 3

Iraeak #Oost reent all last*) ?ile >8stdin+> line ' in 8Oodle+nde!Brror) list assignOent inde! ot of range

# t #i il d i ti f


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#ame typeof error

#imilar description of errorbut with 3assignment4

Progress

5ists

index

*ount from `ero

[" 3 ( 9 '' '3 '9 'R]

priOes[4]

priOes[&]


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223

5ength

2!er-running

len#priOes*

priOes[:]

Deletion del priOes[6]

7xercise ,,

)rack what the !alue of nOersis at each stage of thisse@uence of instructions.

nu=er* ?, #, 11, 13, 1#, 12, 2, 31@+++

nu=er*?1@ 3+++

,

1


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224

T minutes

? @

del nu=er*?3@+++

nu=er*?3@ 3#+++

nu=er*?0@ nu=er*?@+++

6

9

T

ow can we add to a list

list

:

%

int "

list

R

%

int "

#ame list

'ew length


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225

int 'R

int '9

int 'R

int '9

int "37xtra item

Appending to a list

+++ prie*

[" 3 ( 9 '' '3 '9 'R]

+++ prie* (3)+ppend

A function built into a list


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226

+++ prie*

+++ prie*

[" 3 ( 9 '' '3 '9 'R

(3)+ppend.

)he list is now updated

]"3

priOes.append#*

+++ prie* (3)+ppend

)he list

A connecting dot

append#*


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+++ prie* (3)+ppend. append#*

)he !alue to append

All lists ha!e this

function built in.

38ethods4

(arguments)object function.

Beha!es Gustlike a function


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228

a function that has

special access tothe obGect?s data.

sing the append#*method

+++ print(prie*)

[" 3 ( 9 '' '3 '9 'R]

+++ prie* (3)+ppend.

+++ prie* (2)+ppend

)he function doesn?treturn any !alue.


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229



+++ prie* (3#)+ppend.

+++ print(prie*)

[" 3 ( 9 '' '3 '9 'R "3 "R 3' 39]

"t modifiesthe list itself.

2ther methods on lists: reerse#*

+++ nu=er* ?0, #, , 1@

+++ nu=er*.reBer*e()

+++ print(nu=er*)

)he function doesn?treturn any !alue.


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+++ print(nu=er*)

[' ( 9 4]"t modifiesthe list itself.

2ther methods on lists: sort#*

+++ nu=er* ?0, #, , 1@

+++ nu=er*.*ort()

+++ print(nu=er*)

)he function does notreturn the sorted list.


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print(nu=er*)

[' 4 ( 9]

'umerical order.

"t sorts thelist itself.

2ther methods on lists: sort#*

+++ -reeC ?'+lph+', '=et+', '-++', 'delt+'@

+++ -reeC.*ort()

+++ print(-reeC)


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p (- )

[alpha eta delta gaOOa]

Alphabetical order

of the words.

2ther methods on lists: insert#*

+++ -reeC '-++',?'+lph+',

S , 1

+++ -reeC.in*ert(

'delt+'@

here to insert hat to insert

'=et+'1, )


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e e to se t at to se t

+++ -reeC

[alpha gaOOa delta]eta

,Displaced

S

2ther methods on lists: reOoe#*

+++ nu=er* ?#, 0,

+++ nu=er*.reoBe

#, , , 0@",

(")

alueto remo!e


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234

+++ print(nu=er*)

[9 4 9 " ( 4]

c.f. del nOers["] !ndexto remo!e

2ther methods on lists: reOoe#*

+++

+++ nu=er*.reoBe(0)

print(nu=er*)

[9 9 " (4 4]

)here are two instances of 9.


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+++ print(nu=er*)

[9 9 " ( 4]

2nly the first instance is remo!ed

hat methods are there

+++ help(nu=er*)

,elp on list oUet)

lass list#oUet*... append#...*


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236

L.append#oUet* VV append oUet to end...

Pagination:

B

next page

back one page

> @uit

elp on a single method

+++ help(nu=er*.+ppend)

,elp on iltVin fntion append)

append#...* L.append#oUet* VV append oUet to end


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237

#orting a list redux

+++ -reeC ?'+lph+', '=et+', '-++', 'delt+'@

+++ -reeC.*ort() 0ecall: greek.sort#*sorts the list 3in place4.


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+++ print(-reeC)


#orting a list redux: 3sortedKL4

+++ -reeC ?'+lph+', '=et+', '-++', 'delt+'@

+++ print(*orted(-reeC)) sorted#*functionreturns a sorted list%



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239

+++ print(-reeC)

[alpha eta gaOOa delta]

%and lea!es thelist alone

Adding to a list redux: 3;4

+++ prie*

[" 3 ( 9 '' '3 '9 'R]

*oncatenationoperator

5ist to add


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240

+++ prie*

[" 3 ( 9 '' '3 '9 'R

?3, 2, 31@

"3 "R 3']

*oncatenation

+++ newli*t

+++

prie* ?3, 2, 31@

prie* prie* ?3, 2, 31@

*reate a new list

pdate the list


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+++ prie* ?3, 2, 31@

Augmented assignment

*reating lists from text + ,

+++ li*t('Hello')

[, e l l o] list

(

str ' ,

str ' e


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242

str ( , e l l o str ' l

str ' l

str ' o

*reating lists from text + 1

+++ 'Hello, world!'

[,ello world-]

, e l l o w o r l d -'3str

.*plit()

Built in method

#plits on spaces


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243

list

" str 6 , e l l o

str 6 w o r l d -

Progress38ethods4

append#iteO*

reerse#*

sort#*

insert#inde!iteO*

reOoe#iteO*

object.method#arguments*

h l # bj *


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*oncatenation=

=S

['"3] = [4(6]

priOes =S ["R 3']

#orting list.sort#*sorted#list*

elp help#object*help#object.method*

7xercise ,1


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245

T minutes

"s an item in a list + ,

+++ odd* ?3, , #, 2@ Does not include 1

+++ odd*.reoBe()


W l B

ard error

li t # * t i li t

)ry to remo!e 1


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246

WaleBrror) list.reOoe#!*) ! not in list

x must be in thelist before it can

be remo!ed

"s an item in a list + 1+++ odd* ?3, , #, 2@

+++ in odd*

?alse

+++ 3 i dd


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247

+++ 3 in odd*

Ire

+++ not in odd*

Ire

Precedence

!44y !4y!5y!6y !y!y!!

!y !:y!:y!!y !9y!9y

&irst


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248

not! ! or y! +nd y

5ast

! not iny ! in y

)he list now contains

e!ery operator wemeet in this course.

#afe remo!al

if nOer in nOers )

nOers.reOoe#nOer*

hat?s thedifference


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249

while nOer in nOers )

nOers.reOoe#nOer*

orking through a list + ,

e.g. Printing each element on a line

[Ihe at sat on the Oat.]

Ihe


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250

Iheatsatonthe

Oat.

orking through a list + 1

e.g. Adding the elements of a list

[4( 96 V"3 R& '(]

"&3


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251

"&3

hat is the sum of an empty list []

orking through a list + 6

e.g. #@uaring e!ery number in a list

[4 9 V" R ']

['6 4R 4 :' ']


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252

['6 4R 4 :' ']

)he 3for loop4 + ,

words [Ihe at sat on the Oat.]S

for )wordsinword

name of list list

A new Python


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253

for

)wordsinword

print#word*

A new Pythonlooping construct

print: hat we want

to do with the list items.

)he 3for loop4 + 1


for )wordsinword

keywords


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254

for

)wordsinword

print#word*

colon followed byan indented block

)he 3for loop4 + 6


for )wordsinword

Defining the loop %ariable


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255

word*

for )wordsinword

print#

sing the loop !ariable

0unning the 3for loop4

list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word

for )wordsinwordword*print#


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256

str " o n

str 3 t h e

str 4 O a t .

words

&irst loop


list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word



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257

str " o n

str 3 t h e

str 4 O a t .

words

#econd loop


list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word



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258

str " o n

str 3 t h e

str 4 O a t .

words

)hird loop


list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word



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259

str o

str 3 t h e

str 4 O a t .

words

&ourth loop


list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word



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str

str 3 t h e

str 4 O a t .

words

&ifth loop


list

6

str 3 I h e

str 3 a t

str 3 s a t

str " o n

word



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261

str 3 t h e

str 4 O a t .

words

&inal loop

)he 3for loop4 for printing


for )wordsinword


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262

word*print#

for'.py

)he 3for loop4 for adding

nOers S [4( 96 V"3 R& '(]

for )in

total S &

nOer nOers

#et up before the loop


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263

total =S

print#total*

nOer Processing in the loop

0esults after the loop

for".py

)he 3for loop4 for creating a new list

nOers S [4 9 V" R ']

for )in

sares S [ ]

nOer nOers

#et up before the loop


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264

sares.append#

print#sares*

Processing in the loop

0esults after the loop

nOerXX"*

for3.py

)he loop !ariable persistsCnOers S [4 9 V" R ']

for )in

sares.append#

sares S [ ]

nOer nOers

print#

nOerXX"*

*nOer

5oop !ariable onlymeant for use in loopC

But it persistsC


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265

print# *nOer But it persistsC

3for loop hygeine4nOers S [4 9 V" R ']

for )in

sares.append#

sares S [ ]

nOer nOers

del

nOerXX"*

nOer Delete it after use


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266

del nOer Delete it after use

Progress

)esting items in lists

for loops

3 in['"34]

total S &ornOer in['"34]D

total =S nOerdel nOer

Ire


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267

del nOer

loop !ariables for nu=erin ['"34])

total =S nu=erdelnu=er

7xercise ,6

hat does this print

nOers S [& ' " 3 4 (]

total S &

total_so_far S []


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268

T minutes

for nOer in nOers) total =S nOer total_so_far.append#total*

print#total_so_far*

3#ort-of-lists4

Python 3magic4:

)reat it like a list and it will

beha!e like a usefullist


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269

hat can 3it4 be

#trings as lists0ecall:

list#,ello* [, e l l o]

for letter in ,e print#letter* ),ello


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270

llo

p # *

ets turned

into a list.for4.py

*reating lists of numbersBuilt in to Python:

range#startlimit*

for nOer in print#nOer* )range#3:* 34


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p # *(69

[ not included

ranges of numbers'ot actually lists: +++

range#&(*

r+n-e(&,)

But close enough: +++

[& ' " 3 4]

li*t(r+n-e(&,))


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272

[ ]

)reat it like a list and

it will beha!e like a list

hy not Gust a list8ost common use: for nOer in

;range#& '&&&&*)

"nefficient to make ahuge list Gust for this

3iterator4 : anything that can be treated like a list


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273

list#iterator* 7xplicit list

0anges of numbers again

range#'&* [& ' " 3 4 ( 6 9 : R]

range#3 '&* [3 4 ( 6 9 : R]

range#3 '& "* [3 ( 9 R]

!ia list#*

#tart at S

7!ery nth number


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274

range#3 '& "* [3 ( 9 R] 7!ery n number

range#'& 3 V"* ['& : 6 4] 'egati!e steps

"ndices of lists+++ prie* ? , 3, , #, 11, 13, 1#, 12@

+++ len(prie*)

+++ li*t(r+n-e(

:

[& ' " 3 4 ( 6 9]

"))

!alid indices


275/458

275[ ]'R'9'3''9(3 "

96(43"'&

Direct !alue or !ia the indexpriOes S [" 3 ( 9 '' '3 '9 'R]

for priOe in priOes) print#priOe*

#impler


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276

for inde! in range#len#priOes**) print#priOes[inde!]*

7@ui!alent

orking with two lists: 3dot product4

list' S [ &.4]&.&&.3

list" S [ &.6]&.(&."

ZZZ

&."4&.&&.&6 = = &.3

b


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277

orking with two lists: indices

list' S [&.3 &.& &.4]list" S [&." &.( &.6]

for inde! in

sO S &.&

S , 1

indices

)range#len#list'**

li t'[i d ]Xli t"[i d ]


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278

print#sO*

sO =S list'[inde!]Xlist"[inde!]

Dealing with!alues from

both lists atthe same time.

iter

4

"

A little more about iterators + ,

str ( a l p h a

str 4 e t a

+++ -reeC ?'+lph+', '=et+', '-++', 'delt+'@

+++ -reeCEi iter(-reeC)

+++ next(-reeCEi)

alpha 2ffset


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279

str ( g a O O a

str ( d e l t a

+++ next(-reeCEi)

eta

iter

4

A little more about iterators + 1

str ( a l p h a

str 4 e t a

str ( g a O O a

str ( d e l t a

+++ next(-reeCEi)

gaOOa

+++ next(-reeCEi)

delta


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280

str ( d e l t a

+++ next(-reeCEi)

Iraeak #Oost reent all last*) ?ile >8stdin+> line ' in 8Oodle+Atopteration

Progress

'on-lists as lists

3"terators4

range#* range#liOit*range#startliOit*

range#startliOitstep*

range#39* [34(6]

for letter in ,ello) ...

greek_i S iter#greek*

ne!t#greek i*


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"ndices of lists

Parallel lists

for inde! in range#len#things**)

ne!t#greek_i*

7xercise ,9

list' S [ &.4]&.&&.3

list" S [ &.6]&.(&."

V&."V&.(&.'

*omplete e!erise'4.py

Difference

#@uare


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282

T minutes

&.&4&."(&.&' &.3==

#@uare

Add

5ist 3slices4

prie* ?, 3, , #, 11, 13, 1#, 12, 3, 2@

prie*

[" 3 ( 9 '' '3 '9 'R "3 "R]

prie*?3@9

)he list

An item


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283

prie*?3D2@

[9 '' '3 '9 'R "3] "artof the list

#lices + ,

priOes S [" 3 ( 9 '' '3 '9 'R "R 3']

6 \

"3

priOes[ ]R)3

to

fromp to but notincluding%


284/458

284

[9priOes[3)R]

"tem \ notincluded

'' '3 '9 'R "3]

#lices + 1

priOes 9 '' '3 '9 'R "R 3']"3

priOes[ ]R)3 [9 '' '3 '9 'R "3]

[" 3 (

priOes[ ]R) [" 3 ( 9 '' '3 '9 'R "3]

priOes[ ])3 [9 '' '3 '9 'R "3 "R 3']


285/458

285

priOes[ ])3 [9 '' '3 '9 'R "3 "R 3']

priOes[ ]) [" 3 ( 9 '' '3 '9 'R "3 "R 3']

#lices + 6

priOes 9 '' '3 '9 'R "R 3']"3

priOes[ ]R)3 [9 '' '3 '9 'R "3]

[" 3 (

priOes[ )R)3 [9 '3 'R ]]"

priOes[ )R)3 ]3 [9 '9 ]


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286

priOes[ )R)3 ]3 [9 '9 ]

list

3letters

*opies and slices + ,

letter* ?'+','=',''@

str ' a

+lph+=et letter*


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287

alphaet

str '

str '

list

3letters

*opies and slices + 1

letter*?&@ 'F'+++

str ' J

print(+lph+=et)+++

[J ]


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288

alphaet

str '

str '

letters alphaet

list

3


letter* ?'+','=',''@+++

str ' a

+lph+=et letter*?D@+++

list

3

#lices arecopies.


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289

str '

str '


letter*?&@ 'F'+++

print(+lph+=et)+++

#lices arecopies.

[a ]

letters

alphaet

list

3str ' a

list

3str ' F


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290

str '

str '

Progress

#lices

iteOs[froO)to]

iteOs[)to]

iteOs[froO)to)stride]

iteOs[)to)stride]

7nd-limit excluded

#lices are copies


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291

[ ]

iteOs[froO)]

iteOs[)]

[ ]

iteOs[froO))stride]

iteOs[))stride]

7xercise ,T

Predict what this Python will do.)hen run it.ere you right

e!erise'(.py

foo S [4 6 " 9 3 ' R 4 " 9 4 6 & "]

ar S foo[3)'")3]

ar["] =S foo[4]


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292

6 minutes

foo[&] S ar[']

print#ar*

list

(

Di!ersion: 5ists and strings

)ext: 3a strinof characters4

list#*

str ' ,

str ' e

str ' l

str ' l

str ( , e l l o


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293

str ' o

"ndexing into strings

'Hello, world!'?&@+++

,

'Hello, world!'?D0@+++

,ell

#imple indexing

#licing


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294

#trings are immutable

'Hello, world!'?&@ ';'+++

Iraeak #Oost reent all last*) ?ile >8stdin+> line ' in 8Oodle+IypeBrror) str oUet does not spport

iteO assignOent


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295

&iles

.t!t

.dat

.s

"nput 2utput


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.s

0eading riting

0eading a text file

&ile name

&ile obGect

il

treasre.t!t

ook

IHBJAFHB ALJN

string

file

t i

3opening4 the file

reading from the file


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&ile contents IHBJAFHB ALJN string

&inished with the file

3closing4 the file

2pening a text file

+++ =ooC )'r','tre+*ure.txt'(open

0ead-only jtext

&ile name

Python function

Python file obGect

3mode4


298/458

298ook *treasre.t!t#openS

0ead-only isthe default

0eading from a file obGect

+++ line1 =ooC

&ile obGect

&irst line of file

+++ line1 "ncludes the

next( )

3next line( please4


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+++ line1

7nIHBJAFHB ALJN

"ncludes the3end of line4

&ile obGect are iterable

+++ line next(=ooC)

#econd line of file

+++ line

7n

+++ line3 next(=ooC)

A blank line


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+++ line3

PJHI DB7n

)hird line of file

*losing the file

+++ .lo*e()=ooC

8ethod built in to file obGect

&rees the file for otherprograms to write to it.


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)he file obGect + ,

+++ =ooC

8_io.Ie!tDKrapper

enodingSFI?V:+naOeStreasre.t!t

)ext "nput/2utput

&ile name

*haracter encoding:how to representletters as numbers


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letters as numbers.

)he file obGect + 1

file "R treasre.t!t FI?V:

IHBJAFHB ALJN

PJHI DB

Ihe Dld Qaneer

3offset4: how far into

the file we ha!e read

&ile name

)ext encoding


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303

Pointer to the fileon the file system

0eading through a file

)reat it like a list andit will beha!e like a list

list#file_object* 5ist of lines in the file

+++ =ooC open('tre+*ure.txt', 'r')

+++ line* li*t(=ooC)


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304

+++ line* li*t(=ooC)

+++ print(line*)

0eading a file mo!es the offset

C+++ =ooC open('tre+*ure.txt', 'r')

+++ line*E+ li*t(=ooC)

+++ print(line*E+)

+++ line*E= li*t(=ooC)

uge output%


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305

+++ print(line*E=)

[] 7mpty list

0eading a file mo!es the offset

+++ =ooC

+++ line*E+

+++ print(line*E+)

+++

%

&ile obGect starts with offset at start.

open('tre+*ure.txt', 'r')

2peration reads entire file from offset.

li*t(=ooC)

line*E= li*t(=ooC)

2ffset changed to endof file.

i d i fil f ff


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+++ print(line*E=)

[]

2peration reads entire file from offset.

#o thereQs nothing left to read.

0esetting the offset

+++ =ooC

+++ line*E+

+++ print(line*E+)

+++

%

open('tre+*ure.txt', 'r')

li*t(=ooC)

=ooC.*eeC(&) #et the offset explicitly


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+++ line*E= li*t(=ooC)

+++ print(line*E=)

)ypical way to process a file

ook S open#treasre.t!t r*

for line in ook )

%

)reat it like a list%


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308

7xample: lines in a file


n_lines S &

for line in ook )

n_lines =S '

5ine count

0ead each line of the file

"ncrement the count


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309

print#n_lines* Print out the count

ook.lose#*

7xample: characters in a file


n_hars S &

for line in ook )

n_hars len#line*

'umber of characters on the line

"ncrease the count by that many

=S


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print#n_hars*y y

ook.lose#*

Progress

2pening file to read

0eading file

*losing file

&ile offset

ook S open#filenaOe r*

ook.lose#*

ook.seek#&*

for line in ook) ...


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311

7xercise ,U

*omplete a script to countlines( words and characters

of a file.

e!erise'6.py


312/458

312T minutes

riting files

&ile name

Data to write

&ile obGect

treasre.t!t

ook

IHBJAFHB ALJN

string

file

string

3opening4 the file

writing to the file


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&inished with the file

3closing4 the file

2pening a text file for writing

+++ output )'w','output.txt'(open

2pen for

writing jtext

)hi ill t t


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314C

)his will truncatean existing file

2pening a text file for appending

+++ output )'+','output.txt'(open

2pen for

appending jtext


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riting to a file obGect + ,

+++ .writeoutput

8ethod built into file obGect

&ile obGect

(line1)

Data being written6

'umber ofcharactersactually written


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316

actually written

+++ len(line1)

6

riting to a file obGect + 1

+++ .writeoutput ('+lph+ )ypical use: whole line.

"ncludes 3end of line4

%n')

+++ .writeoutput ('=e')

+++ .writeoutput ('t+%n')

Doesn?t ha!eto be whole lines

+++ writeoutput ('-++%ndelt+%n')

6

"

3


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317

+++ .writeoutput ('-++%ndelt+%n')

*an be multiple lines

'"

*losing the file obGect

+++ .lo*e()output Eital for written files


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318

"mportance of closing

Data 3flushed4 to disc on closure.

write 3flush4

C


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319Python script &ile obGect &ile system

"mportance of closingpromptly

C&iles locked for other accessopen jQwQ open jQrQ


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320

K8ore a problem for indows than nixL

riting non-text !alues

+++ output.write('/oo!%n') riting text KstrL

(

+++ output.write(0) riting non-text KintL

Iraeak #Oost reent all last*)

?ile >8stdin+> line ' in 8Oodle+IypeBrror) Ost e str not int

write#*only accepts text


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321

riting non-text !alues

+++ output.write( *on!ert to text: str#*

"

+++ output.write('%n') 7xplicit end-of-line

'

*tr(0))


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322

)ext formatting Klater in the courseL

pro!ides a more elegant solution.

Progress

2pening files for writing

7xplicit ends of lines

ook S open#filenaOe w*

ook.write#7n*

riting data ook.write#str#data**

riting text ook.write#te!t*


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323*losing the file is important ook.lose#*

7xercise ,V

)he script e!erise'9.pyprintsa series of numbers ending in ,.

*hange the script to write to a file calledotpt.t!tinstead of printing to the console.


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324T minutes

&unctions

y = f(

x)


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325

&unctions we ha!e met

print#line*

open#filename mode*

range#from to, stride*

float#thing*

int#thing*

iter#list*

str#thing*

len#thing*

type#thing*

inpt#prompt*

ool#thing*

ord#char*

hr#number*

list#thing*


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326

# g*

'ot that manyC 3)he Python ay4:"f it is appropriate to an obGect(make it a method of that obGect.

# *

Whywrite our own functions

% read

% test

% fix

% impro!e

% add to

% write

7asier to %

3#tructuredprogramming4


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327

programming

% de!elop

Defining a function

(y1, y2, y3) (x1, x2, x3, x4, x5)= f

Identifythe inputs

Identifythe processing

Identifythe outputs


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328

A function to define: total#*

#um a list

j,( 1( 6

jV( -9( ,( U( S

j

U

,S

S 37dge case4


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329

j

Defining a Python function + ,

def )# ; *total colon

inputs

name of function

define a function called %


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330

Defining a Python function + 1

def total# *)nOers

name for the input

)his name isinternaltothe function.


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331


def total#nOers*) *olon followed by indentation


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332


def total#nOers*)

sO_so_far S &

for nOer in nOers) sO_so_far =S nOer 3Body4 of function


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333


def total# *)nOers

sO_so_far

forsO_so_far =S nOer

S &

in nOers)nOer

)hese !ariables exist onlywithin the function?s body.


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334

Defining a Python function + T

def total#nOers*)

sO_so_far S &

for nOer in nOers) sO_so_far =S nOer

retrn sO_so_far)his !alueis returned


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335returnthis !alue

Defining a Python function + U

def total#nOers*)

sO_so_far S &


retrn sO_so_far

And that$s it%


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336

nindented

after this

Defining a Python function + V

And that$s it%

All internal names cleaned up 'o need for del

All internal names internal 'o need to a!oid reusing names


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337

sing a Python function + ,def total#nOers*)

sO_so_far S &


retrn sO_so_far

print#total#[' " 3]**

)he list wewant to add up


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338

want to add up

sing a Python function + 1def total#nOers*)

sO_so_far S &


retrn sO_so_far


)he function weha!e Gust written


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339

G


sO_so_far S &

for nOer in nOers)

sO_so_far =S nOer

retrn sO_so_far


Printing outthe answer


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340


sO_so_far S &

for nOer in nOers)

sO_so_far =S nOer

retrn sO_so_far


$ python3 tot+l1.py

6

nb: nix prompt


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341total'.py

sing a Python function + Tdef total#nOers*)

sO_so_far S &

for nOer in nOers)

sO_so_far =S nOer

retrn sO_so_far

print#total#[' " 3]**print#total#[9V4'6&]**print#total#[]**

$ python3 tot+l.py

6'&&

se the functionmultiple times


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342total".py

&unctions? pri!ate names + ,def total#nOers*)

sO_so_far S &

for nOer in nOers)

sO_so_far =S nOer

retrn sO_so_far

data S [' " 3]data_sO S total#data*pr

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