Python Basics

Python is powerful… and fast; plays well with others; runs everywhere; is friendly & easy to learn; is Open.

(https://www.python.org/about/)

Installing

Details on how to install Python can be found at (https://www.python.org/downloads/).

Printing

Printing lets you output something like a word or some numbers and even more. The print() function will display the given value on screen.

# This will display Hello, World!
print("Hello, World!")

You can also put mathematical expressions inside the print function and Python will solve the expression and print the answer.

# This will display 4
print(2 + 2)

This can be combined with other operators and variables (both covered further down) and it can be fun to play around with these to see what happens.

Comments

Comments allow you to type something out without Python thinking you’re writing code. Usually you’ll use comments to explain what certain methods or lines of code do. Python has 2 ways to do comments but only 1 will be shown here as the other is only really used in a situation that will be covered later.

# This is an inline comment, everything after the # on the same line will be commented out.
# Usually you'll use these to describe what a line of code is doing.

Data Types

Python has many different ways to represent different forms of data. If you wanted to create a sentence, you would use a str, or string, data type. Numbers can be separated into int, or integer, for whole numbers, and float for numbers with decimals. Another data type is called a bool or a boolean. This type is a simple True or False. There are many more types than this, but these are a few of the basics ones.

String str:

• “Hello, World!”
• “Blue”
• “1”
• “1.0”
• “True”

Integer int:

• 1
• 10
• -1
• 0

Float float:

• 1.0
• 0.0
• -1.0
• 3.14159
• 2.718281828

Boolean bool:

• True
• False

Variables

Variables allow you to store values for later use. This can be helpful when you want to use the same value multiple times, and can make the code more readable.

Creating and updating variables uses the same syntax so make sure you aren’t accidentally creating a new variable instead of updating a current one, or vice versa.

This is how you create and update variables:

x_position = 10.5

is_flipped = False

name = "Alice"

You can then use these later in the code. For example, if you wanted print the name variable:

name = "Alice"

print(name)

This program will display the word Alice.

Tip

It is important to give variables names that make sense for what they do. For example, if you have a String variable of someone’s name, name would be a good name for it, and n would not be as it does not describe what the value means. This makes the code more readable and more understandable to someone else that reads your code.

According to the Python style guide, variable names should be in snake_case where all letters are lowercase, and underscores should be used in place of spaces.

Operators

Operators allow you to create expressions that give you a result, like a mathematical equation for example. There are a few different types of operators in Python.

Arithmetic Operators

Arithmetic operators allow you to write equations that will return a value.

Examples:

• + Addition
• - Subtraction
• * Multiplication
• / Division
• % Modulus
• ** Exponentiation
• // Floor Division

x + y # Adds x and y

x - y # Subtracts y from x

x * y # Multiplies x with y

x / y # Divides x by y

x % y # Gives the remainder of x divided by y

x ** y # Raises x to the power of y

x // y # Divides x by y and then rounds down to the nearest whole number

Note

Some of these operators can also be used with other types, such as Strings. For example, adding two Strings together will combine them into one ("Hello, " + "World!" will give you "Hello, World!). With the String type, only + and * can be used. Play around with operators and other types and see what happens.

Assignment Operators

Assignment operators allow you to assign values to variables.

Examples:

• =
• +=
• -=
• *=
• /=
• %=
• **=
• //=

x = 5 # Gives x the value of 5

x += 5 # Gives x the value of x + 5

# E.g.
x = 5 # Set x to 5
x += 10 # This is the same as x = x + 10, or x = 5 + 10 in this example. So x is now given the value of 15

# The following operators follow the above rule

x -= 5 # Gives x the value of x - 5

x *= 5 # Gives x the value of x * 5

x /= 5 # Gives x the value of x / 5

x %= 5 # Gives x the value of x % 5

x **= 5 # Gives x the value of x ** 5

x //= 5 # Gives x the value of x // 5

Comparison Operators

Comparison operators allow you to compare values and variables with each other. These will return a bool type, a True or False result.

Examples:

• == Equals
• != Not Equals
• > Greater Than
• < Less Than
• >= Greater Than or Equal To
• <= Less Than or Equal To

x == y # Is the value of x equal to the value of y

x != y # Is the value of x not equal to the value of y

x > y # Is the value of x greater than the value of y

x < y # Is the value of x less than the value of y

x >= y # Is the value of x greater than or equal to the value of y

x <= y # Is the value of x less than or equal to the value of y

Logical Operators

Logical operators allows you to compare bool values with each other .

Example:

• and
• or
• not

x > 5 and x < 10 # Will return True only if both x is greater than 5 and less than 10

x > 5 or x < 10 # Will return True if at least one of the statements is True

not x > 5 # If x is greater than 5, this will return False, if x is not greater than 5, this will return True
# This essentially flips a True to a False and vice versa

Note

Comparison and Logical operators are used more often with if statements and loops. These will be covered in later guides.