PythonLet’s get started!
Getting Started
• Two modes: • Interactive
• Script ** we will be working in script mode for the most part
Running a program
• Open IDLE
• File New Window
• File Save (add “.py” to your file, it may not add it automatically)
• Run Run Module
Functions
• A “function” is a pre-written code that will perform a specific task
• Python comes with a number of pre-written functions, but you can also write your own (as we will later on in this class)
• Functions begin with a keyword and are followed by a set of parentheses
• Ex: print ( )
Functions
• Functions can pass what we call “arguments”, which are placed inside the parentheses of the function
• Ex: print (“Hello, world!”)
• Different functions will expect different types of arguments (more on types of arguments later)
• When you use a function on python, we say we are “calling” a function
Types of Data
• There are three types of data that we will use in Python for our purposes • Strings: textual data
• Integers: numerical data, restricted to integers
• Floats: numerical data, decimals included
Strings
• A string is data that is textual in nature
• Strings can contain none or some characters
• “String literals” are strings defined within your program/function and must be “delimited” by a special character which tells Python to treat it as textual data, and not as a function • Ex: print (“Hello, world!”)
• Ex: print (“print”)
Delimiters
• Python recognizes three types of delimiters• The single “tick” : ( ‘ hello ’ )
• The single “quote” : ( “ hey there! ” )
• The triple quote : ( “”” what’s up dude “”” )
Print Challenge
• Try to write a Python program that prints the following lines of text:
Hello, my name is Bruce!
Hi, Bruce!
Fish are friends, not food!
Print Function
• You’ll notice that the print function will automatically add a line break after it prints your argument
• “”” the triple quote delimiters can be used for data that is on multiple lines
Printing multiple arguments
• The print function can accept none or multiple arguments at a time
• Multiple arguments can be separated by a comma
• Example: print (“Hello!”, ‘my name is’, “Donald”)
• The print function will automatically insert a space between any two arguments (we will learn how to avoid this later on)
Commenting your program
• As we mentioned, your programs can become very long, so you will want to write comments either for yourself or another user
• Python recognizes the symbol # as a commentator symbol, so it will ignore everything that comes after that symbol on the same line
# First, I will ask the user for their name, I will then store it in a variable called “x”
x = input (“What is your name?”)
# Now, I will print the name of the user
print (x)
Multi-line comments
• You can also input multi-line comments on Python using the triple quote delimiter
“””
Python will ignore this line
And this line
And this one too
“””
print (“Hello, world!”)
Comments as Pseudocode
• Comments are often used as pseudocode in order to outline the task at hand
• Ex:
#get two test scores from user
# add test scores
# divide by 2
# print out result
Comments as a debugging technique
• Comments can be used for debugging because Python will ignore portions of your code
• Debugging means to identify and to remove any errors in your code
# I don’t know why this one isn’t working!
# print ( ‘ Hello, world! ” )
Variables
• Variables are like buckets that hold and store information in your computer’s memory
• You can create a variable by using the following syntax: • variablename = data
Examples: speed = 5
name = “Donald”
• The “=” is the assignment operator and it tells Python to store data on right of operator into variable, named on the left of the operator
Rules on naming variables
• You cannot use reserved words (they are listed on the next slide)
• Variable names can’t contain spaces but they can contain an underscore “_”
• The first character of a variable name must be a letter or an underscore, it cannot be a numerical value
• Python is case sensitive (variablename vs. VariableName)
Reserved words
• These words cannot be used as variable names:
False, True, None, and, as, assert, break, class, continued, def, del, elif, else, except, finally, for, from, global, if, import, in, is, lambda, nonlocal, not, or, pass, raise, return, try, while, with, yield
(you’ll notice, True, False, None have capital letters)
• Reserved words will show up in a different color while writing in script mode
Examples
class = 2
Class = 2
classAvg = 24
_class_avg = 42
2ndclassAvg = 56
classavg! = 99
Examples
class = 2 illegal (reserved word)
Class = 2 legal
classAvg = 24 legal
_class_avg = 42 legal
2ndclassAvg = 56 illegal (can’t start with a number)
classavg! = 99 illegal (only alphanumeric values, and “_” )
Common Variable Naming Techniques
• Some variable names can be hard to read, so there are common techniques that are used to distinguish them:
cartopspeed = 140 # hard to read …
car_top_speed = 140
carTopSpeed = 140
car_top_speed_3 = 140
Printing variables
• You can print the data that is stored within a variable by passing the variable as an argument into the print function
name = “Donald” name = Donald
print (name) print (“Hello, my name is”, name)
>> Donald >> Hello, my name is Donald
Changing variables
• Variables are called variables because the data stored in them can be changed
• You can change the value/data stored in a variable with a second assigning statement
dollars = 19.99
print (“I have”, dollars, “in my account”)
dollars = 10000.99
print (“Now, I have”, dollars, “in my account”)
Multiple Assignments
• You can assign multiple variables on the same line:
x, y, z = 1, 2, 3
# the variables will assume the values in order
• You can also assign the same value to multiple variables
x = y = z = 10
# variables x, y, and z will all hold the value of 10
Practice
• You’re working on a simple inventory management system for a small store. You’d like to store the name and price of two products and print them, so that your inventory page looks something like this:
Item: Bread, price: $ 1.99
Item: Eggs, price: $ 3.49