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template <typename T>

_Defer<void(*(PID<T>, void (T::*)(void)))

(const PID<T>&, void (T::*)(void))>

defer(const PID<T>& pid, void (T::*method)(void))

{

void (*dispatch)(const PID<T>&, void (T::*)(void)) =

&process::template dispatch<T>;

return std::tr1::bind(dispatch, pid, method);

}

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print("Hello world")

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import requests

resp = requests.get("https://realpython.com")

html = resp.text

print(html[205:294])

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<title>Python Tutorials – Real Python</title>

<meta name="author" content="Real Python">

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https://insights.stackoverflow.com/trends?tags=c%23%2Cjava%2Cjavascript%2Cpython%2Cc%2B%2B

https://insights.stackoverflow.com/survey/2018/

https://insights.stackoverflow.com/survey/2018/

https://insights.stackoverflow.com/survey/2018/#technology-most-loved-dreaded-and-wanted-languages

https://insights.stackoverflow.com/survey/2018/#technology-most-loved-dreaded-and-wanted-languages

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#include <stdio.h>

int main(void)

{

printf("Hello, world\n");

}

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print("Hello, world")

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Python 3.7.2 (default, Dec 25 2018, 03:50:46)

[GCC 7.3.0] on linux

Type "help", "copyright", "credits" or "license()" for more information.

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��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiYzZPRHpHaFF6SnVnaHlCZmdofC16MGU1QmU-NDFfKFY3aUxQZ2NoUyIsInQiOiJjaGFwdGVycy8wMy8wMi5tZCAoMzExOWVkMDAzZDU4MzIwMykiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi8zMTE5ZWQwMDNkNTgzMjAzMThkYmEyYTc5OWIzMjMxODc3ZDBlMDVlL2NoYXB0ZXJzLzAzLzAyLm1kIn0=


4ZOUBY &SSPST

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print("Hello, world)

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EOL while scanning string literal.

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��


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print(Hello, world)

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Traceback (most recent call last):

File "/home/hello_world.py", line 1, in <module>

print(Hello, world)

NameError: name 'Hello' is not defined

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ύ " NameError PDDVSSFE�

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��

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��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoidWRNMipAeENIb1E5aSQyP2VnVEkpIUI1aUR7e1k8O1dvPTl1eXozXiIsInQiOiJjaGFwdGVycy8wMy8wMy5tZCAoNmFjM2M3NDExNmU5ZWUzOCkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi82YWMzYzc0MTE2ZTllZTM4ODRmMzVlMjFiODY2YjU5N2M4NTNiMmVlL2NoYXB0ZXJzLzAzLzAzLm1kIn0=


phrase = "Hello, world"

print(phrase)

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/PUF

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print("phrase")

��


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Phrase = "Hello, world"

print(phrase)

$BO ZPV TQPU UIF EJмFSFODF *O UIJT FYBNQMF UIF нSTU MJOF EFнOFT

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��


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��

https://en.wikipedia.org/wiki/Unicode

https://docs.python.org/3/howto/unicode.html#python-s-unicode-support


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https://pep8.org

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>>> my_phrase = "Hello, world"

>>> my_phrase

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print(my_phrase)�

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>>> print(my_phrase)

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��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoic19eMXQ-bTBQNFghbkFvJilxUm5TK31neWYmZX10X0NTfilQNVU5YCIsInQiOiJjaGFwdGVycy8wMy8wNC5tZCAoYjRhYjc4YmEyNjUyYjFjOSkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi9iNGFiNzhiYTI2NTJiMWM5MTY2MjUxNWQ3MDBhYzkwMGY0YWNiMmYzL2NoYXB0ZXJzLzAzLzA0Lm1kIn0=

�� *OTQFDU 7BMVFT JO UIF *OUFSBDUJWF 8JOEPX

8IFO ZPV KVTU UZQF my_phrase BOE QSFTT Enter ZPV BSF UFMMJOH 1ZUIPO UP

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TFOUBUJPO PG UIF PCKFDU BTTJHOFE UP UIF WBSJBCMF� *O UIJT DBTF my_phrase

JT B SFGFSFODF UP UIF TUSJOH "Hello, world" TP UIF PVUQVU JT TVSSPVOEFE

XJUI TJOHMF RVPUFT UP JOEJDBUF UIBU JU JT B TUSJOH PCKFDU�

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>>> x = 2

>>> x

2

>>> print(x)

2

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>>> x = 2

>>> y = "2"

>>> print(x)

2

��

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>>> print(y)

2

>>> x

2

>>> y

'2'

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>>> print

<built-in function print>

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my_phrase = "Hello, world"

my_phrase

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# This is my first script

phrase = "Hello, world."

print(phrase) # This line displays "Hello, world"

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# Print "Hello, world"


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"""

This is my first script.

��

�� 4VNNBSZ BOE "EEJUJPOBM 3FTPVSDFT

It prints the phrase "Hello, world."

The comments are longer than the script!

"""

phrase = "Hello, world."

print(phrase)

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print("Hello, world") """This is

an invalid comment"""

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https://pep8.org


https://realpython.com/python-beginner-tips/

https://realpython.com/python-comments-guide/

https://realpython.com/python-basics/resources/#recommended-resources

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiUFRnVFNER2o_bD9DZV9XbDFsbEdHREZyJXdqXnNqQnZTelcmJjF8cCIsInQiOiJjaGFwdGVycy8wMy8wNy5tZCAoODQyMjhkNDA5YjBhODhiMikiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi84NDIyOGQ0MDliMGE4OGIyMzBmM2VlNDlhOTc1YzU2N2RmOWEwMDE4L2NoYXB0ZXJzLzAzLzA3Lm1kIn0=

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string1 = 'Hello, world.'

string2 = "We're #1!"

string3 = "1234"

string4 = 'I said, "Put it over by the llama."'

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>>> text = "She said "What time is it?""

File "<stdin>", line 1

text = "She said "What time is it?""

^

SyntaxError: invalid syntax

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paragraph = "This planet has - or rather had - a problem, which was \

this: most of the people living on it were unhappy for pretty much \

of the time. Many solutions were suggested for this problem, but \

most of these were largely concerned with the movements of small \

green pieces of paper, which is odd because on the whole it wasn't \

the small green pieces of paper that were unhappy."

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paragraph = """This planet has - or rather had - a problem, which was

this: most of the people living on it were unhappy for pretty much

of the time. Many solutions were suggested for this problem, but

most of these were largely concerned with the movements of small

green pieces of paper, which is odd because on the whole it wasn't

the small green pieces of paper that were unhappy."""

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>>> print("""This is a

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... that also preserves whitespace.""")

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https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiSkxDVDhQfnhubGYoIT9rKm9OQms-fk99VmprQlhJR28hKzEtY0dCViIsInQiOiJjaGFwdGVycy8wNC8wMi5tZCAoM2RlMjdiNDc0ZTJiYjZhOSkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi8zZGUyN2I0NzRlMmJiNmE5YTg3ZWRmOGZkNzEzOTFlMmI2ZDcxYjllL2NoYXB0ZXJzLzA0LzAyLm1kIn0=


>>> string1 = "abra"

>>> string2 = "cadabra"

>>> magic_string = string1 + string2

>>> magic_string

'abracadabra'

*O UIF FYBNQMF BCPWF TUSJOH DPODBUFOBUJPO PDDVST PO UIF UIJSE MJOF

XIFSF string1 BOE string2 BSF DPODBUFOBUFE VTJOH + BOE UIF SFTVMU JT

BTTJHOFE UP UIF WBSJBCMF magic_string� /PUJDF UIBU UIF UXP TUSJOHT BSF

KPJOFE UPHFUIFS XJUIPVU BOZ XIJUFTQBDF CFUXFFO UIFN�

0OF DPNNPO BQQMJDBUJPO PG TUSJOH DPODBUFOBUJPO JT UP KPJO UXP SFMBUFE

TUSJOHT TVDI BT B нSTU BOE MBTU OBNF JOUP B GVMM OBNF�

>>> first_name = "Jean-Luc"

>>> last_name = "Picard"

>>> full_name = first_name + " " + last_name

>>> full_name

'Jean-Luc Picard"

*O UIJT FYBNQMF B TQBDF JT BEEFE CFUXFFO UIF first_name BOE last_name

TUSJOHT CZ нSTU DPODBUFOBUJOH first_nameXJUI " " BOE UIFO DPODBUFOBU�

JOH UIF SFTVMU XJUI last_name�

8IFO ZPV XBOU UP DPNCJOF NBOZ TUSJOHT BU PODF JOTJEF PG B print()

GVODUJPO ZPV DBO BMTP VTF DPNNBT UP TFQBSBUF UIFN� 5IJT BVUPNBUJ�

DBMMZ BEET TQBDFT CFUXFFO UIF TUSJOHT MJLF TP�

>>> print("abra", "ca", "dabra")

abra ca dabra

5IF DPNNBT IBWF UP HP PVUTJEF PG UIF RVPUBUJPO NBSLT TJODF PUIFS�

XJTF UIF DPNNBT XPVME CFDPNF QBSU PG UIF TUSJOHT UIFNTFMWFT�

��


/PUF

5FDIOJDBMMZ TQFBLJOH XIFO ZPV print() NVMUJQMF TUSJOHT TFQB�

SBUFE CZ B DPNNB ZPV BSFOυU QFSGPSNJOH TUSJOH DPODBUFOBUJPO

CFDBVTF ZPV BSFOυU VTJOH UIF + PQFSBUPS� 5IJT UFDIOJRVF DBO CF

VTFGVM IPXFWFS XIFO ZPV OFFE UP EJTQMBZ TFWFSBM TUSJOHT PO UIF

TBNF MJOF BOE ZPV EPOυU XBOU UP DPODBUFOBUF UIFN JOUP B OFX

TUSJOH�

%FUFSNJOF UIF -FOHUI PG B 4USJOH

5IF MFOHUI PG B TUSJOH JT UIF OVNCFS PG DIBSBDUFST DPOUBJOFE JO UIF

TUSJOH JODMVEJOH TQBDFT� 'PS FYBNQMF UIF TUSJOH "abc" IBT MFOHUI �

BOE UIF TUSJOH "make it so" IBT MFOHUI ��

5P EFUFSNJOF UIF MFOHUI PG B TUSJOH VTF 1ZUIPOυT CVJMU�JO len() GVOD�

UJPO� 5P TFF IPX JU XPSLT UZQF UIF GPMMPXJOH JOUP *%-&υT JOUFSBDUJWF

XJOEPX�

>>> len("abc")

3

:PV DBO VTF len() UP HFU UIF MFOHUI PG TUSJOHT UIBU IBWF CFFO BTTJHOFE

UP B WBSJBCMF�

>>> my_string = "abc"

>>> string_length = len(my_string)

>>> string_length

3

'JSTU UIF TUSJOH "abc" JT BTTJHOFE UP UIF WBSJBCMF my_string� 5IFO len()

JT VTFE UP HFU UIF MFOHUI PG my_string BOE BTTJHO UIJT WBMVF UP UIF

string_length WBSJBCMF� 'JOBMMZ UIF WBMVF PG string_length XIJDI JT �

JT EJTQMBZFE�

/PUJDF IPX my_string JT QMBDFE CFUXFFO UIF UXP QBSFOUIFTFT PG UIF

len() GVODUJPO� 5IJT UFMMT len() UP QFSGPSN JUT PQFSBUJPO XJUI UIF my_-

��


string WBSJBCMF UIF TBNF XBZ UIBU QVUUJOH B TUSJOH JO CFUXFFO UIF

QBSFOUIFTFT PG print() UFMMT 1ZUIPO UP QSJOU UIF TUSJOH�

"DDFTT $IBSBDUFST JO B 4USJOH

" TUSJOH JT B TFRVFODF PG DIBSBDUFST� :PV DBO BDDFTT JOEJWJEVBM DIBSBD�

UFST JO B TUSJOH CZ UBDLJOH PO TRVBSF CSBDLFUT [ BOE ] BGUFS UIF TUSJOH

BOE QVUUJOH B OVNCFS O JO CFUXFFO UIF CSBDLFUT UP HFU UIF OUI DIBSBD�

UFS JO UIF TUSJOH�

8BSOJOH

#F DBSFGVM XIFO ZPVυSF VTJOH�

ύ QBSFOUIFTFT� ( )

ύ TRVBSF CSBDLFUT� [ ]

ύ DVSMZ CSBDFT� { }

5IFTF BMM NFBO EJмFSFOU UIJOHT JO 1ZUIPO TP ZPV DBO OFWFS

TXJUDI POF GPS BOPUIFS� :PVυMM TFF NPSF FYBNQMFT PG XIFO FBDI

POF JT VTFE BT ZPV QSPHSFTT UISPVHI UIJT CPPL� 'PS OPX KVTU CF

BXBSF UIFZυSF BMM VTFE EJмFSFOUMZ�

5ZQF UIF GPMMPXJOH JOUP *%-&υT JOUFSBDUJWF XJOEPX�

>>> flavor = "apple pie"

>>> flavor[3]

'l'

5ZQJOH flavor[3] SFUVSOT UIF UIJSE DIBSBDUFS PG UIF TUSJOH "apple pie"

XIJDI JTώ "l" 8BJU JTOυU 'p' UIF UIJSE DIBSBDUFS PG "apple pie"

*O 1ZUIPOρBOE NPTU PUIFS QSPHSBNNJOH MBOHVBHFTρDPVOUJOH

BMXBZT TUBSUT BU �� 4P JO UIJT DBTF 'a' JT UIF ψ[FSPUIω DIBSBDUFS PG UIF

TUSJOH "apple pie"� 5IVT 'p' JT UIF нSTU DIBSBDUFS 'p' JT UIF TFDPOE

BOE 'l' JT UIF UIJSE�

��


5P EJTQMBZ UIF ψнSTUω DIBSBDUFS ZPV OFFE UP QSJOU UIF �UI DIBSBDUFS�

>>> flavor[0]

'a'

5IF OVNCFS BTTJHOFE UP FBDI DIBSBDUFSυT QPTJUJPO JT DBMMFE UIF DIBSBD�

UFSυT JOEFY PS TVCTDSJQU OVNCFS� 5IF GPMMPXJOH UBCMF TIPXT FBDI

DIBSBDUFS PG UIF TUSJOH "apple pie" BOE JUT BTTPDJBUFE JOEFY�

$IBSBDUFS� a p p l e p i e

*OEFY�4VCTDSJQU� 0 1 2 3 4 5 6 7 8

8BSOJOH

'PSHFUUJOH UIBU DPVOUJOH TUBSUT XJUI [FSP BOE USZJOH UP SFGFS UP

UIF нSTU DIBSBDUFS JO B TUSJOH XJUI UIF JOEFY 1 SFTVMUT JO XIBU JT

DPNNPOMZ LOPXO BT BO Pп�CZ�POF FSSPS�

0м�CZ�POF FSSPST BSF B DPNNPO TPVSDF PG GSVTUSBUJPO GPS CFHJO�

OJOH BOE FYQFSJFODFE QSPHSBNNFST BMJLF�

8IBU EP ZPV UIJOL IBQQFOT JG ZPV USZ UP BDDFTT B DIBSBDUFS CZ BO JOEFY

UIBU JT HSFBUFS UIBO UIF JOEFY PG UIF MBTU DIBSBDUFS JO UIF TUSJOH 5SZ

UIJT PVU�

>>> flavor[13]


File "<stdin>", line 1, in <module>

IndexError: string index out of range

1ZUIPO UISPXT BO IndexError UFMMJOH ZPV UIBU UIF JOEFY JT ψPVU PG SBOHF�ω

5IF MBSHFTU JOEFY UIBU ZPV DBO BDDFTT JO B TUSJOH JT POF MFTT UIBO UIF

MFOHUI PG UIF TUSJOH� 4JODF "apple pie" IBT MFOHUI � UIF MBSHFTU JOEFY

ZPV DBO BDDFTT JT ��

��


-FUυT USZ TPNFUIJOH FWFO DSB[JFS� 8IBU EP ZPV UIJOL IBQQFOT JG ZPV

USZ UP BDDFTT B OFHBUJWF JOEFY (JWF UIJT B USZ�

>>> flavor[-1]

'e'

5IF JOEFY �� JT BTTPDJBUFE UP UIF MBTU DIBSBDUFS JO UIF TUSJOH XIJDI GPS

"apple pie" JT UIF MFUUFS "e"� 5IF OFHBUJWF JOEJDFT GPS UIF DIBSBDUFST JO

UIF TUSJOH "apple pie" BSF TIPXO JO UIF UBCMF CFMPX�

$IBSBDUFS� a p p l e p i e

/FHBUJWF JOEFY� -9 -8 -7 -6 -5 -4 -3 -2 -1

4VQQPTF ZPV OFFE UIF TUSJOH DPOUBJOJOH KVTU UIF нSTU UISFF MFUUFST PG

UIF TUSJOH flavor = "apple pie"� :PV DPVME BDDFTT FBDI DIBSBDUFS CZ

JOEFY BOE DPODBUFOBUF UIFN MJLF UIJT�

>>> first_three_letters = flavor[0] + flavor[1] + flavor[2]

>>> first_three_letters

'app'

:PV DBOQSPCBCMZ JNBHJOF IPX DMVNTZ UIJTXPVME CF GPS FYUSBDUJOH MPUT

PG JOGPSNBUJPO GSPN B MPOH TUSJOH� *U JT VTVBMMZ FBTJFS UP HFU QPSUJPOT

PG B TUSJOH VTJOH TMJDFT�

4USJOH 4MJDFT

:PV DBO FYUSBDU B QPSUJPO PG B TUSJOH DBMMFE B TVCTUSJOH XJUI BO FY�

UFOEFE WFSTJPO PG UIF TVCTDSJQU PQFSBUJPO� 5P EP UIJT JOTFSU B DPMPO

CFUXFFO UXP TVCTDSJQU OVNCFST JOTJEF PG TRVBSF CSBDLFUT MJLF UIJT�


>>> flavor[0:3]

'app'

��


5IF FYQSFTTJPO flavor[0:3] SFUVSOT UIF нSTU UISFF DIBSBDUFST PG UIF

TUSJOH BTTJHOFE UP UIF WBSJBCMF flavor TUBSUJOH BU UIF �UI DIBSBDUFS BOE

HPJOH VQ UP CVU OPU JODMVEJOH UIF �SE DIBSBDUFS� 5IF [0:3] QBSU PG

flavor[0:3] JT DBMMFE B TMJDF TJODF JU SFUVSOT B ψTMJDFω PG UIF TUSJOH SFG�

FSFODFE CZ UIF WBSJBCMF flavor� *O UIJT DBTF JU SFUVSOT B TMJDF PG "apple

pie"� :VN�

5IF OVNCFS CFGPSF UIF DPMPO JO B TMJDF JT BMXBZT UIF JOEFY PG UIF нSTU

DIBSBDUFS UP JODMVEF XIJMF UIF OVNCFS BGUFS UIF DPMPO JT UIF JOEFY

PG UIF нSTU DIBSBDUFS UIBU JTOυU JODMVEFE� *G ZPV VTF UIF DPMPO JO UIF

CSBDLFUT CVU PNJU POF PG UIF OVNCFST JO B SBOHF 1ZUIPO BTTVNFT UIBU

ZPV XBOU UP HP BMM UIF XBZ UP UIF FOE PG UIF TUSJOH JO UIBU EJSFDUJPO�


>>> flavor[:5]

'apple'

>>> flavor[5:]

' pie'

>>> flavor[:]

'apple pie'

4MJDFT BMTP TVQQPSU OFHBUJWF JOEJDFT�

>>> flavor[:-5]

'appl'

>>> flavor[-5:]

'e pie'

>>> flavor[-8:-5]

'ppl'

*G ZPV USZ UP BDDFTT BO JOEFY JO B TMJDF UIBU EPFTOυU FYJTU 1ZUIPO XPOυU

UISPX BO IndexError MJLF JU EPFT JG ZPV USZ UP HFU B TJOHMF DIBSBDUFS�

>>> flavor[:14]

'apple pie'

��


>>> flavor[13:15]

''

*O UIJT FYBNQMF UIF нSTU MJOF HFUT UIF TMJDF GSPN UIF CFHJOOJOH PG UIF

TUSJOH VQ UP CVU OPU JODMVEJOH UIF GPVSUFFOUI DIBSBDUFS� 5IF TUSJOH

BTTJHOFE UP flavor IBT MFOHUI � TP ZPV NJHIU FYQFDU 1ZUIPO UP UISPX

BO FSSPS� *OTUFBE BOZ OPO�FYJTUFOU JOEJDFT BSF JHOPSFE BOE UIF FOUJSF

TUSJOH "apple pie" JT SFUVSOFE�

5IF TFDPOE MJOF PG UIF FYBNQMF TIPXT XIBU IBQQFOT XIFO ZPV USZ UP

HFU B TMJDF XIFSF UIF FOUJSF SBOHF JT PVU PG CPVOET� flavor[13:15] BU�

UFNQUT UP HFU UIF UIJSUFFOUI BOE GPVSUFFOUI DIBSBDUFST XIJDI EPOυU

FYJTU� *OTUFBE PG UISPXJOH BO FSSPS UIF FNQUZ TUSJOH "" JT SFUVSOFE�

4USJOHT "SF *NNVUBCMF

5P XSBQ UIJT TFDUJPO VQ MFUυT EJTDVTT BO JNQPSUBOU QSPQFSUZ PG TUSJOH

PCKFDUT� 4USJOHT BSF JNNVUBCMF XIJDI NFBOT UIBU ZPV DBOυU DIBOHF

UIFN PODF ZPVυWF DSFBUFE UIFN� 'PS JOTUBODF TFF XIBU IBQQFOT XIFO

ZPV USZ UP BTTJHO B OFX MFUUFS UP POF QBSUJDVMBS DIBSBDUFS PG B TUSJOH�

>>> my_string = "goal"

>>> my_string[0] = "f" # This won't work!



TypeError: 'str' object does not support item assignment

1ZUIPO UISPXT B TypeError BOE UFMMT ZPV UIBU str PCKFDUT EPOυU TVQQPSU

JUFN BTTJHONFOU�

/PUF

5IF UFSN str JT 1ZUIPOυT JOUFSOBM OBNF GPS UIF TUSJOH EBUB UZQF�

*G ZPV XBOU UP BMUFS B TUSJOH ZPV NVTU DSFBUF BO FOUJSFMZ OFX TUSJOH�

5P DIBOHF UIF TUSJOH "goal" UP UIF TUSJOH "foal" ZPV DBO VTF B TUSJOH

��

�� 6TF 4USJOH .FUIPET

TMJDF UP DPODBUFOBUF UIF MFUUFS "f"XJUI FWFSZUIJOH CVU UIF нSTU MFUUFS PG

UIF XPSE "goal"�

>>> my_string = "goal"

>>> my_string = "f" + my_string[1:]

>>> my_string

'foal'

'JSTU BTTJHO UIF TUSJOH "goal" UP UIF WBSJBCMF my_string� 5IFO DPODBUF�

OBUF UIF TMJDF my_string[1:] XIJDI JT UIF TUSJOH "oal" XJUI UIF MFUUFS "f"

UP HFU UIF TUSJOH "foal"� *G ZPVυSF HFUUJOH B EJмFSFOU SFTVMU IFSF NBLF

TVSF ZPVυSF JODMVEJOH UIF : DPMPO DIBSBDUFS BT QBSU PG UIF TUSJOH TMJDF�

3FWJFX &YFSDJTFT

�� $SFBUF B TUSJOH BOE QSJOU JUT MFOHUI VTJOH UIF len() GVODUJPO�

�� $SFBUF UXP TUSJOHT DPODBUFOBUF UIFN BOE QSJOU UIF SFTVMUJOH

TUSJOH�

�� $SFBUF UXP TUSJOH WBSJBCMFT UIFO QSJOU POF PG UIFN BGUFS UIF PUIFS

XJUI B TQBDF BEEFE JO CFUXFFO VTJOH B DPNNB JO ZPVS QSJOU TUBUF�

NFOU�

�� 3FQFBU FYFSDJTF � CVU JOTUFBE PG VTJOH DPNNBT JO print() VTF DPO�

DBUFOBUJPO UP BEE B TQBDF CFUXFFO UIF UXP TUSJOHT�

�� 1SJOU UIF TUSJOH "zing" CZ VTJOH TVCTDSJQUT BOE JOEFY OVNCFST PO

UIF TUSJOH "bazinga" UP TQFDJGZ UIF DPSSFDU SBOHF PG DIBSBDUFST�



5IF 1ZUIPO QSPHSBNNJOH MBOHVBHF JT BO FYBNQMF PG BO PCKFDU�

PSJFOUFE MBOHVBHF XIJDI NFBOT UIBU EBUB JT TUPSFE JO PCKFDUT� "

TUSJOH JT BO FYBNQMF PG BO PCKFDU� %POυU XPSSZ UPP NVDI BCPVU XIBU JU

NFBOT UP CF BO PCKFDU� 8IBU JT JNQPSUBOU GPS SJHIU OPX JT UIBU PCKFDUT

��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiS2FwQ3pGTnIwOzI4R3FAMUZJR2JpfCVjaHJOM3I3ekFaKGZqQXNFWSIsInQiOiJjaGFwdGVycy8wNC8wMy5tZCAoY2JiZGM4MzA2ZjRmMzM5NykiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi9jYmJkYzgzMDZmNGYzMzk3Mzg5YmQzMTg2NTBkNGRlZWVjOGQ0ZDk3L2NoYXB0ZXJzLzA0LzAzLm1kIn0=


IBWF CPUI EBUB BOE GVODUJPOTρDBMMFE NFUIPETρUIBU BSF VTFE UP

XPSL XJUI UIF EBUB�

*O UIJT TFDUJPO ZPV XJMM MFBSO BCPVU TPNF PG UIF NFUIPET UIBU DBO CF

VTFE UP NBOJQVMBUF TUSJOHT� *O QBSUJDVMBS ZPV XJMM MFBSO IPX UP DPO�

WFSU B TUSJOH UP VQQFS PS MPXFS DBTF IPX UP SFNPWF XIJUFTQBDF GSPN

TUSJOH BOE IPX UP EFUFSNJOF JG B TUSJOH DPOUBJOT POMZ OVNCFST�

$POWFSUJOH 4USJOH $BTF

5P DPOWFSU B TUSJOH UP BMM MPXFS DBTF MFUUFST ZPVVTF UIF TUSJOHυT .lower()

NFUIPE� 5IJT JT EPOF CZ UBDLJOH .lower() PO UP UIF FOE PG UIF TUSJOH

JUTFMG�

>>> "Arthur Dent".lower()

'arthur dent'

5IF . UFMMT 1ZUIPO UIBU XIBU GPMMPXT JT UIF OBNF PG B NFUIPEρUIF

lowerNFUIPE JO UIJT DBTF� 5IF QBSFOUIFTFT () BGUFS UIFNFUIPEυT OBNF

UFMM 1ZUIPO UP FYFDVUF UIF NFUIPE KVTU MJLF QBSFOUIFTFT BSF VTFE UP

FYFDVUF UIF print() BOE len() GVODUJPOT�

4USJOH NFUIPET EPOυU KVTU XPSL PO TUSJOH MJUFSBMT� :PV DBO VTF UIF

.lower() NFUIPE PO B WBSJBCMF OBNF UIBU JT BTTJHOFE UP B TUSJOH BT

XFMM�

>>> name = "Arthur Dent"

>>> name.lower()

'arthur dent'

5IF DPVOUFSQBSU UP UIF .lower()NFUIPE JT UIF .upper()NFUIPE XIJDI

DPOWFSUT FWFSZ DIBSBDUFS JO B TUSJOH UP VQQFS DBTF�

>>> loud_voice = "Can you hear me yet?"

>>> loud_voice.upper()

'CAN YOU HEAR ME YET?'

��


$PNQBSF UIF .upper() BOE .lower() TUSJOH NFUIPET UP UIF HFOFSBM�

QVSQPTF len() GVODUJPO ZPV TBX JO UIF MBTU TFDUJPO� "TJEF GSPN UIF

EJмFSFOU SFTVMUT PG UIFTF GVODUJPOT UIF JNQPSUBOU EJTUJODUJPO IFSF JT

IPX UIFZ BSF VTFE�

5IF len() GVODUJPO EPFTOυU CFMPOH UP BO PCKFDU� *G ZPV XBOU UP EFUFS�

NJOF UIF MFOHUI PG UIF loud_voice TUSJOH ZPV DBMM UIF len() GVODUJPO

EJSFDUMZ MJLF UIJT�

>>> len(loud_voice)

20

0O UIF PUIFS IBOE .upper() BOE .lower()NVTU CF VTFE JO DPOKVODUJPO

XJUI B TUSJOH PCKFDU� 5IFZ EP OPU FYJTU JOEFQFOEFOUMZ�

/PUF

5ISPVHIPVU UIJT CPPL ZPV XJMM TFF OVNFSPVT FYBNQMFT PG PC�

KFDUNFUIPET� 8IFO SFGFSSJOH UPNFUIPET JO B QBSBHSBQI PG UFYU

UIFZXJMM CF QSFGBDFEXJUI B . EPU TVDI BT .lower() BOE .upper()�

UP JOEJDBUF UIBU UIFZ BSF NFUIPET PG BO PCKFDU BOE OPU HFOFSBM

QVSQPTF GVODUJPOT�

4PNFUJNFT UIF NFUIPEυT QBSFOU PCKFDU JT JODMVEFE JO UIF SFG�

FSFODF UP NBLF JU DMFBS XIJDI PCKFDU UIF NFUIPE CFMPOHT UPρ

GPS FYBNQMF loud_voice.upper()� )PXFWFS UIJT CPPL VTFT UIF

TIPSUFS .upper() TUZMF PG SFGFSSJOH UP BNFUIPEXIFOFWFS UIF DPO�

UFYU JT DMFBS�

3FNPWJOH8IJUFTQBDF 'SPN B 4USJOH

8IJUFTQBDF JT BOZ DIBSBDUFS UIBU JT QSJOUFE BT CMBOL TQBDF� 5IJT JO�

DMVEFT UIJOHT MJLF TQBDFT BOE MJOF GFFET XIJDI BSF TQFDJBM DIBSBDUFST

UIBU NPWF PVUQVU UP B OFX MJOF�

4PNFUJNFT ZPV OFFE UP SFNPWF XIJUFTQBDF GSPN UIF CFHJOOJOH PS FOE

PG B TUSJOH� 5IJT JT FTQFDJBMMZ VTFGVM XIFO XPSLJOH XJUI TUSJOHT UIBU

��


DPNF GSPN VTFS JOQVU XIFSF FYUSB XIJUFTQBDF DIBSBDUFST NBZ IBWF

CFFO JOUSPEVDFE CZ BDDJEFOU�

5IFSF BSF UISFF TUSJOHNFUIPET UIBU ZPV DBO VTF UP SFNPWF XIJUFTQBDF

GSPN B TUSJOH� .rstrip() .lstrip() BOE .strip()� 5IF нSTU PG UIFTF

.rstrip() SFNPWFT XIJUFTQBDF GSPN UIF SJHIU TJEF PG B TUSJOH�

>>> name = "Arthur Dent "

>>> name

'Arthur Dent '

>>> name.rstrip()

'Arthur Dent'

*O UIJT FYBNQMF UIF TUSJOH "Arthur Dent " IBT нWF USBJMJOH TQBDFT�

1ZUIPO EPFTOυU SFNPWF BOZ USBJMJOH TQBDFT JO B TUSJOH BVUPNBUJDBMMZ

XIFO UIF TUSJOH JT BTTJHOFE UP B WBSJBCMF� 5IF .rstrip() NFUIPE SF�

NPWFT USBJMJOH TQBDFT GSPN UIF SJHIU�IBOE TJEF PG UIF TUSJOH BOE SF�

UVSOT B OFX TUSJOH "Arthur Dent" XIJDI OP MPOHFS IBT UIF TQBDFT BU UIF

FOE�

5IF .lstrip()NFUIPE XPSLT KVTU MJLF .rstrip() FYDFQU UIBU JU SFNPWFT

XIJUFTQBDF GSPN UIF MFGU�IBOE TJEF PG UIF TUSJOH�

>>> name = " Arthur Dent"

>>> name

' Arthur Dent'

>>> name.lstrip()

'Arthur Dent'

5P SFNPWF XIJUFTQBDF GSPN CPUI UIF MFGU BOE UIF SJHIU TJEFT PG UIF

TUSJOH BU UIF TBNF UJNF VTF UIF .strip() NFUIPE�

>>> name = " Arthur Dent "

>>> name

' Arthur Dent '

>>> name.strip()

'Arthur Dent'

��


/PUF

/POF PG UIF .rstrip() .lstrip() BOE .strip() NFUIPET SFNPWF

XIJUFTQBDF GSPN UIF NJEEMF PG UIF TUSJOH XIJDI ZPV DBO TFF JO

UIF QSFWJPVT FYBNQMFT CFDBVTF UIF TQBDF CFUXFFO ψ"SUIVSω BOE

ψ%FOUω JT QSFTFSWFE FBDI UJNF�

%FUFSNJOF JG B 4USJOH 4UBSUT PS &OET8JUI B 4USJOH

" DPNNPO QSPCMFN XIFO XPSLJOH XJUI TUSJOHT JT UP EFUFSNJOF JG

B HJWFO TUSJOH TUBSUT XJUI PS FOET XJUI DFSUBJO DIBSBDUFST� :PV DBO

VTF UXP TUSJOH NFUIPET UP TPMWF UIJT QSPCMFN� .startswith() BOE

.endswith()�

-FUυT MPPL BU BO FYBNQMF� $POTJEFS UIF TUSJOH "Enterprise"� )FSFυT IPX

ZPV VTF .startswith() UP EFUFSNJOF JG UIF TUSJOH TUBSUT XJUI UIF MFUUFST

"e" BOE "n"�

>>> starship = "Enterprise"

>>> starship.startswith("en")

False

:PVNVTU UFMM .startswith()XIBU DIBSBDUFST UP TFBSDI GPS CZ QSPWJEJOH

B TUSJOH DPOUBJOJOH UIPTF DIBSBDUFST� 4P UP EFUFSNJOF JG "Enterprise"

TUBSUT XJUI UIF MFUUFST "e" BOE "n" ZPV DBMM .startswith("en")� 5IJT SF�

UVSOTώ False 8IZ EP ZPV UIJOL UIBU JT

*G ZPV HVFTTFE UIBU .startswith("en") SFUVSOT False CFDBVTF "En-

terprise" TUBSUT XJUI B DBQJUBM "E" ZPVυSF BCTPMVUFMZ SJHIU� 5IF

.startswith() NFUIPE JT DBTF�TFOTJUJWF� 5P HFU .startswith() UP

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>>> starship.startswith("En")

True

5IF .endswith() NFUIPE JT VTFE UP EFUFSNJOF JG B TUSJOH FOET XJUI DFS�

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��


>>> starship.endswith("rise")

True

+VTU MJLF .startswith() UIF .endswith() NFUIPE JT DBTF�TFOTJUJWF�

>>> starship.endswith("risE")

False

/PUF

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>>> name = "Elena"

>>> name.upper()

'ELENA'

>>> name

'Elena'

8IFO ZPV DBMM name.upper() OPUIJOH BCPVU name BDUVBMMZ DIBOHFT� *G

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>>> name = "Elena"

>>> name = name.upper()

��


>>> name

'ELENA'

name.upper() SFUVSOT B OFX TUSJOH "ELENA" XIJDI JT SF�BTTJHOFE UP UIF

name WBSJBCMF� 5IJT PWFSSJEFT UIF PSJHJOBM TUSJOH "Elena" BTTJHOFE UP

"name"�

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EVDFE JO UIJT TFDUJPO POMZ TDSBUDI UIF TVSGBDF� *%-& DBO BDUVBMMZ IFMQ

ZPV нOE OFX TUSJOH NFUIPET� 5P TFF IPX нSTU BTTJHO B TUSJOH MJUFSBM

UP B WBSJBCMF JO UIF JOUFSBDUJWF XJOEPX�

>>> my_string = "kerfuffle"

5ZQF my_string GPMMPXFE CZ B QFSJPE CVU EP OPU IJU Enter� :PV TIPVME

TFF UIF GPMMPXJOH JO UIF JOUFSBDUJWF XJOEPX�

>>> my_string.

/PX IJU Ctrl+Space� *%-& EJTQMBZT B MJTU PG FWFSZ TUSJOH NFUIPE UIBU

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ZPV POMZ UZQF JO my_string.u BOE UIFO IJU UIF Tab LFZ *%-& BVUPNBUJ�

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5IJT FWFO XPSLT XJUI WBSJBCMF OBNFT� 5SZ UZQJOH JO KVTU UIF нSTU GFX

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my_string GPS ZPV XIFO ZPV IJU UIF 5"# LFZ�

��

�� *OUFSBDU 8JUI 6TFS *OQVU

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�� 8SJUF B TDSJQU UIBU DPOWFSUT UIF GPMMPXJOH TUSJOHT UP MPXFSDBTF� "An-

imals" "Badger" "Honey Bee" "Honeybadger"� 1SJOU FBDI MPXFSDBTF

TUSJOH�

�� 3FQFBU &YFSDJTF � CVU DPOWFSU FBDI TUSJOH UP VQQFSDBTF JOTUFBE PG

MPXFSDBTF�

�� 8SJUF B TDSJQU UIBU SFNPWFT XIJUFTQBDF GSPN UIF GPMMPXJOH TUSJOHT�

string1 = " Filet Mignon"

string2 = "Brisket "

string3 = " Cheeseburger "

1SJOU PVU UIF TUSJOHT XJUI UIF XIJUFTQBDF SFNPWFE�

�� 8SJUF B TDSJQU UIBU QSJOUT PVU UIF SFTVMU PG .startswith("be") PO FBDI

PG UIF GPMMPXJOH TUSJOHT�

string1 = "Becomes"

string2 = "becomes"

string3 = "BEAR"

string4 = " bEautiful"

�� 6TJOH UIF TBNF GPVS TUSJOHT GSPN &YFSDJTF � XSJUF B TDSJQU UIBU

VTFT TUSJOH NFUIPET UP BMUFS FBDI TUSJOH TP UIBU .startswith("be")

SFUVSOT True GPS BMM PG UIFN�



/PX UIBU ZPVυWF TFFO IPX UP XPSL XJUI TUSJOH NFUIPET MFUυT NBLF

UIJOHT JOUFSBDUJWF� *O UIJT TFDUJPO ZPVXJMM MFBSO IPX UP HFU TPNF JOQVU

GSPN B VTFS XJUI UIF input() GVODUJPO� :PVυMM XSJUF B QSPHSBN UIBU BTLT

B VTFS UP JOQVU TPNF UFYU BOE UIFO EJTQMBZ UIBU UFYU CBDL UP UIFN JO

VQQFSDBTF�

5P VTF UIF input() GVODUJPO ZPV NVTU TQFDJGZ B QSPNQU� 5IF QSPNQU

JT KVTU B TUSJOH UIBU ZPV QVU JO CFUXFFO UIF QBSFOUIFTFT PG input()� *U

��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiMWFPO3k5IWp5RGt3TUs2NWMyVil5c3taS0I9VmtaQkxiWWRofWhySiIsInQiOiJjaGFwdGVycy8wNC8wNC5tZCAoNTUwZGFiMDczMTdjOTlhYSkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi81NTBkYWIwNzMxN2M5OWFhMDQ0NDg3NjI3ZDE3YWFmZjhjNjUwNTA3L2NoYXB0ZXJzLzA0LzA0Lm1kIn0=


DBO CF BOZUIJOH ZPV XBOU� B XPSE B TZNCPM B QISBTFρBOZUIJOH UIBU

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5IF input() GVODUJPO EJTQMBZT UIF QSPNQU BOEXBJUT GPS UIF VTFS UP UZQF

TPNFUIJOH PO UIFJS LFZCPBSE� 8IFO UIF VTFS IJUT Enter input() SF�

UVSOT UIFJS JOQVU BT B TUSJOH UIBU DBO CF BTTJHOFE UP B WBSJBCMF BOE

VTFE UP EP TPNFUIJOH JO ZPVS QSPHSBN�

5P TFF IPX input() XPSLT TBWF BOE SVO UIF GPMMPXJOH TDSJQU�

prompt = "Hey, what's up? "

user_input = input(prompt)

print("You said:", user_input)

8IFO ZPV SVO UIJT TDSJQU ZPVυMM TFF Hey, what's up? EJTQMBZFE JO UIF

JOUFSBDUJWF XJOEPXXJUI B CMJOLJOH DVSTPS� 5IF TJOHMF TQBDF BU UIF FOE

PG UIF TUSJOH "Hey, what's up " NBLFT TVSF UIBU XIFO UIF VTFS TUBSUT

UP UZQF UIF UFYU JT TFQBSBUFE GSPN UIF QSPNQU XJUI B TQBDF� 8IFO

ZPV UZQF B SFTQPOTF BOE QSFTT Enter ZPVS SFTQPOTF JT BTTJHOFE UP UIF

user_input WBSJBCMF�

)FSFυT B TBNQMF SVO PG UIF QSPHSBN�

Hey, what's up? Mind your own business.

You said: Mind your own business.

0ODF ZPV IBWF JOQVU GSPN B VTFS ZPV DBO EP TPNFUIJOH XJUI JU� 'PS

FYBNQMF UIF GPMMPXJOH TDSJQU UBLFT VTFS JOQVU BOE ψTIPVUTω JU CBDL

CZ DPOWFSUJOH UIF JOQVU UP VQQFSDBTF XJUI .upper() BOE QSJOUJOH UIF

SFTVMU�

response = input("What should I shout? ")

response = response.upper()

print("Well, if you insist...", response)

��

�� $IBMMFOHF� 1JDL "QBSU :PVS 6TFSυT *OQVU

3FWJFX &YFSDJTFT

�� 8SJUF B TDSJQU UIBU UBLFT JOQVU GSPN UIF VTFS BOE EJTQMBZT UIBU JO�

QVU CBDL�

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JO MPXFSDBTF�

�� 8SJUF B TDSJQU UIBU UBLFT JOQVU GSPN UIF VTFS BOE EJTQMBZT UIF OVN�

CFS PG DIBSBDUFST JOQVUUFE�


�� $IBMMFOHF� 1JDL "QBSU :PVS 6TFSφT

*OQVU

8SJUF B TDSJQU OBNFE first_letter.py UIBU нSTU QSPNQUT UIF VTFS GPS

JOQVU CZ VTJOH UIF TUSJOH� Tell me your password: 5IF TDSJQU TIPVME

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UP VQQFS�DBTF BOE EJTQMBZ JU CBDL�

'PS FYBNQMF JG UIF VTFS JOQVU JT "no" UIFO UIF QSPHSBN TIPVME SFTQPOE

MJLF UIJT�

The first letter you entered was: N

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JOH BT JOQVUρUIBU JT UIFZ KVTU IJU Enter JOTUFBE PG UZQJOH TPNFUIJOH JO�

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BO VQDPNJOH DIBQUFS�


�� 8PSLJOH8JUI 4USJOHT BOE /VNCFST

8IFOZPV HFU VTFS JOQVU VTJOH UIF input() GVODUJPO UIF SFTVMU JT BMXBZT

B TUSJOH� 5IFSF BSFNBOZ PUIFS UJNFT XIFO JOQVU JT HJWFO UP B QSPHSBN

��

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiQVpnSDYyZnxUIXN1dGF1cFcxKTFRdWw1NV9jZUd-K1NCWEFsYjJ8QyIsInQiOiJjaGFwdGVycy8wNC8wNS5tZCAoZmMzNWU1NDY3OTBlYjQ5ZSkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi9mYzM1ZTU0Njc5MGViNDllOWRmYTUyMWE4NWQxMzMxMWYzODE2MDA1L2NoYXB0ZXJzLzA0LzA1Lm1kIn0=

https://feedback.realpython.com/rp-book1-early-access/?d=eyJwIjoicnAtYm9vazEtZWFybHktYWNjZXNzIiwic2lnIjoiVzRYUz11OVkwYzJ1SVV0dFAmZmFebyM_a0hzJVIwOX40Q0dMVUBCNCIsInQiOiJjaGFwdGVycy8wNC8wNi5tZCAoMDM5MmU4NzRlZDllZWNkOSkiLCJ1IjoiaHR0cHM6Ly9naXRodWIuY29tL3JlYWxweXRob24vYm9vazEvYmxvYi8wMzkyZTg3NGVkOWVlY2Q5OTM2NjZlMzUxZTE4MGM2ZjQwODA2MTY1L2NoYXB0ZXJzLzA0LzA2Lm1kIn0=

�� 8PSLJOH 8JUI 4USJOHT BOE /VNCFST

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GFE JOUP DBMDVMBUJPOT�

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XJMM TFF IPXBSJUINFUJD PQFSBUJPOTXPSL PO TUSJOHT BOEIPX UIFZ PGUFO

MFBE UP TVSQSJTJOH SFTVMUT� :PV XJMM BMTP MFBSO IPX UP DPOWFSU CFUXFFO

TUSJOHT BOE OVNCFS UZQFT�

4USJOHT BOE "SJUINFUJD 0QFSBUPST

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UJWF XJOEPX�

>>> num = "2"

>>> num + num

'22'

5IF + PQFSBUPS XIFO VTFE XJUI UXP TUSJOHT DPODBUFOBUFT TUSJOHT UP�

HFUIFS� 4P UIF SFTVMU PG "2" + "2" JT "22" OPU "4"�

4USJOHT DBO CF ψNVMUJQMJFEω CZ BO JOUFHFS� 5ZQF UIF GPMMPXJOH JOUP UIF

JOUFSBDUJWF XJOEPX�

>>> num = "12"

>>> num * 3

'121212'

5IF FYQSFTTJPO num * 3 DPODBUFOBUFT UIF TUSJOH SFGFSFODFE CZ "12"XJUI

JUTFMG � UJNFT BOE SFUVSOT UIF TUSJOH "121212"� 5P DPNQBSF UIJT PQFSB�

UJPO UP BSJUINFUJD XJUI OVNCFST OPUJDF UIBU "12" * 3 = "12" + "12" +

"12"� *O PUIFS XPSET NVMUJQMZJOH B TUSJOH CZ BO JOUFHFS n DPODBUFOBUFT

UIBU TUSJOH XJUI JUTFMG n UJNFT�

5IF OVNCFS PO UIF SJHIU�IBOE TJEF PG UIF FYQSFTTJPO num * 3 DBO CF

NPWFE UP UIF MFGU BOE UIF SFTVMU JT VODIBOHFE�

��


>>> 3 * num

'121212'

8IBU EP ZPV UIJOL IBQQFOT JG ZPV VTF UIF * PQFSBUPS CFUXFFO UXP

TUSJOHT 5ZQF "12" * "3" JO JO UIF JOUFSBDUJWF XJOEPX BOE QSFTT En-

ter�

>>> "12" * "3"



TypeError: can't multiply sequence by non-int of type 'str'

1ZUIPO UISPXT B TypeError BOE UFMMT ZPV UIBU ZPV DBOυU NVMUJQMZ B TF�

RVFODF CZ B OPO�JOUFHFS� 8IFO UIF * PQFSBUPS JT VTFE XJUI B TUSJOH

PO FJUIFS UIF MFGU PS UIF SJHIU TJEF JU BMXBZT FYQFDUT BO JOUFHFS PO UIF

PUIFS TJEF�

/PUF

" TFRVFODF JT BOZ 1ZUIPO PCKFDU UIBU TVQQPSUT BDDFTTJOH FMF�

NFOUT CZ TVCTDSJQU� 4USJOHT BSF TFRVFODFT� :PVXJMM MFBSO BCPVU

PUIFS TFRVFODF UZQFT JO $IBQUFS ��

8IBU EP ZPV UIJOL IBQQFOT XIFO ZPV USZ UP BEE B TUSJOH UP B OVNCFS

>>> "3" + 3



TypeError: can only concatenate str (not "int") to str

"HBJO 1ZUIPO UISPXT B TypeError CFDBVTF UIF + PQFSBUPS FYQFDUT CPUI

UIJOHT PO FJUIFS TJEF PG JU UP CF PG UIF TBNF UZQF� *G BOZ POF PG UIF

PCKFDUT PO FJUIFS TJEF PG + JT B TUSJOH 1ZUIPO USJFT UP QFSGPSN TUSJOH

DPODBUFOBUJPO� "EEJUJPO XJMM POMZ CF QFSGPSNFE JG CPUI PCKFDUT BSF

OVNCFST� 4P UP BEE "3" + 3 BOE HFU 6 ZPV NVTU нSTU DPOWFSU UIF

TUSJOH "3" UP B OVNCFS�

��


$POWFSUJOH 4USJOHT UP /VNCFST

5IF TypeError FSSPST ZPV TBX JO UIF QSFWJPVT TFDUJPO IJHIMJHIU B DPN�

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OVNCFS BOE OPU B TUSJOH�

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num = input("Enter a number to be doubled: ")

doubled_num = num * 2

print(doubled_num)

8IFO ZPV FOUFS B OVNCFS TVDI BT � ZPV FYQFDU UIF PVUQVU UP CF � CVU

JO UIJT DBTF ZPV HFU �� 3FNFNCFS input() BMXBZT SFUVSOT B TUSJOH TP

JG ZPV JOQVU � UIFO num JT BTTJHOFE UP UIF TUSJOH "2" OPU UIF JOUFHFS 2�

5IFSFGPSF UIF FYQSFTTJPO num * 2 SFUVSOT UIF TUSJOH "2" DPODBUFOBUFE

XJUI JUTFMG XIJDI JT "22"�

*O PSEFS UP QFSGPSN BSJUINFUJD PO OVNCFST UIBU BSF DPOUBJOFE JO B

TUSJOH ZPV NVTU нSTU DPOWFSU UIFN GSPN B TUSJOH UZQF UP B OVNCFS

UZQF� 5IFSF BSF UXP XBZT UP EP UIJT� int() BOE float()�

int() TUBOET GPS ψJOUFHFSω BOE DPOWFSUT PCKFDUT JOUP XIPMF OVNCFST

XIJMF float() TUBOET GPS ψGMPBUJOH�QPJOU OVNCFSω BOE DPOWFSUT PCKFDUT

JOUP OVNCFST XJUI EFDJNBM QPJOUT� )FSFυT XIBU VTJOH UIFN MPPLT MJLF

JO UIF JOUFSBDUJWF XJOEPX�

>>> int("12")

12

>>> float("12")

12.0

/PUJDF IPX float() BEET B EFDJNBM QPJOU UP UIF OVNCFS� 'MPBUJOH�

QPJOU OVNCFST BMXBZT IBWF BU MFBTU POF EFDJNBM QMBDF PG QSFDJTJPO� 'PS

UIJT SFBTPO ZPV DBOυU DIBOHF B TUSJOH UIBU MPPLT MJLF B GMPBUJOH�QPJOU

��


OVNCFS JOUP BO JOUFHFS CFDBVTF ZPV XPVME MPTF FWFSZUIJOH BGUFS UIF

EFDJNBM QPJOU�

>>> int("12.0")



ValueError: invalid literal for int() with base 10: '12.0'

&WFO UIPVHI UIF FYUSB � BGUFS UIF EFDJNBM QMBDF EPFTOυU BEE BOZ WBMVF

UP UIF OVNCFS 1ZUIPO XPOυU DIBOHF �� JOUP �� CFDBVTF JU XPVME

SFTVMU JO UIF MPTT PG QSFDJTJPO�

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UP нY JU� )FSFυT UIF TDSJQU BHBJO�


doubled_num = num * 2

print(doubled_num)

5IF JTTVF MJFT JO UIF MJOF doubled_num = num * 2 CFDBVTF num SFGFSFODFT

B TUSJOH BOE 2 JT BO JOUFHFS� :PV DBO нY UIF QSPCMFN CZ XSBQQJOH num

XJUI FJUIFS int() PS float()� 4JODF UIF QSPNQUT BTLT UIF VTFS UP JOQVU B

OVNCFS BOE OPU TQFDJнDBMMZ BO JOUFHFS MFUυT DPOWFSU num UP B GMPBUJOH�

QPJOU OVNCFS�


doubled_num = float(num) * 2

print(doubled_num)

/PX XIFO ZPV SVO UIJT TDSJQU BOE JOQVU � ZPV HFU �� BT FYQFDUFE�

5SZ JU PVU�

��


$POWFSUJOH /VNCFST UP 4USJOHT

4PNFUJNFT ZPV OFFE UP DPOWFSU B OVNCFS UP B TUSJOH� :PV NJHIU EP

UIJT GPS FYBNQMF JG ZPV OFFE UP CVJME B TUSJOH GSPN TPNF QSF�FYJTUJOH

WBSJBCMFT UIBU BSF BTTJHOFE UP OVNFSJD WBMVFT�

"T ZPVυWF BMSFBEZ TFFO UIF GPMMPXJOH QSPEVDFT B TypeError�

>>> num_pancakes = 10

>>> "I am going to eat " + num_pancakes + " pancakes."



TypeError: can only concatenate str (not "int") to str

4JODF num_pancakes JT B OVNCFS 1ZUIPO DBOυU DPODBUFOBUF JU XJUI UIF

TUSJOH "I'm going to eat"� 5P CVJME UIF TUSJOH ZPV OFFE UP DPOWFSU

num_pancakes UP B TUSJOH VTJOH str()�

>>> num_pancakes = 10

>>> "I am going to eat " + str(num_pancakes) + " pancakes."

'I am going to eat 10 pancakes.'

:PV DBO BMTP DBMM str() PO B OVNCFS MJUFSBM�

>>> "I am going to eat " + str(10) + " pancakes."

'I am going to eat 10 pancakes.'

str() DBO FWFO IBOEMF BSJUINFUJD FYQSFTTJPOT�

>>> total_pancakes = 10

>>> pancakes_eaten = 5

>>> "Only " + str(total_pancakes - pancakes_eaten) + " pancakes left."

"Only 5 pancakes left."

:PVυSF OPU MJNJUFE UP OVNCFST XIFO VTJOH str()� :PV DBO QBTT JU BMM

TPSUT PG PCKFDUT UP HFU UIFJS TUSJOH SFQSFTFOUBUJPOT�

��


>>> str(print)

'<built-in function print>'

>>> str(int)

"<class 'int'>"

>>> str(float)

"<class 'float'>"

5IFTF FYBNQMFTNBZ OPU TFFN WFSZ VTFGVM CVU UIFZ JMMVTUSBUF IPX GMFY�

JCMF str() JT�

*O UIF OFYU TFDUJPO ZPVυMM MFBSO IPX UP GPSNBU TUSJOHT OFBUMZ UP EJTQMBZ

WBMVFT JO B OJDF SFBEBCMFNBOOFS� #FGPSF ZPVNPWF PO UIPVHI DIFDL

ZPVS VOEFSTUBOEJOH XJUI UIF GPMMPXJOH SFWJFX FYFSDJTFT�

3FWJFX &YFSDJTFT

�� $SFBUF B TUSJOH DPOUBJOJOH BO JOUFHFS UIFO DPOWFSU UIBU TUSJOH JOUP

BO BDUVBM JOUFHFS PCKFDU VTJOH int()� 5FTU UIBU ZPVS OFX PCKFDU JT

B OVNCFS CZ NVMUJQMZJOH JU CZ BOPUIFS OVNCFS BOE EJTQMBZJOH UIF

SFTVMU�

�� 3FQFBU UIF QSFWJPVT FYFSDJTF CVU VTF B GMPBUJOH�QPJOU OVNCFS BOE

float()�

�� $SFBUF B TUSJOH PCKFDU BOE BO JOUFHFS PCKFDU UIFO EJTQMBZ UIFN TJEF�

CZ�TJEF XJUI B TJOHMF QSJOU TUBUFNFOU CZ VTJOH UIF str() GVODUJPO�

�� 8SJUF B TDSJQU UIBU HFUT UXP OVNCFST GSPN UIF VTFS VTJOH UIF

input() GVODUJPO UXJDF NVMUJQMJFT UIF OVNCFST UPHFUIFS BOE

EJTQMBZT UIF SFTVMU� *G UIF VTFS FOUFST � BOE � ZPVS PVUQVU TIPVME

MPPL MJLF�

The product of 2 and 4 is 8.0.


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