Syntax

A variable is created as follows:

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variableName = value

Where variableName is the name of our variable, and the value is the thing that we want the variable to bind to.

Info

This creates a box in memory. variableName will be used as a reference to that spot. variableName will bind to value i.e. gets assigned to that value.

Naming Rules

Each programming language puts some rules for how the a variable could be named. In Python we have the following rules:

1. Start with a letter [a-zA-Z] or an underscore _, but never a digit.
2. Followed by any letter, digit or underscore.
3. A name should not be a reserved keyword if, for, while,…

Note

Python variable names are case-sensitive, meaning that myVar is not the same as myvar.

Python 3 allows Unicode variable names, however we need to take into consideration the following:

1. Allowed characters are the ones that are classified as “like” alphanumeric and underscore.
2. Certain Unicode letters are not allowed, such as mathematical operations (+, -,..), emoji, and special characters like @, #, or spaces

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x = 3
2
age = 21
3
num_1 = 30
4
first = -5
5
_second = 13
6
π = 3.1415
7
علي = "Me"

It feels weird to have your name in Arabic as a variable name, but it is what it is.

Integer

Integer is a non-decimal number. It can be positive, or negative.

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x = 10
2
y = -200
3
z = 12345678912345678123456789123456789
4
t = 0

Note

The integer implementation in Python has unlimited precision.

String

A string is a sequence of characters enclosed with single quotations ' or double quotations ".

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var = "Hey!"
2
courseName = "Python Fundamentals"
3
welcome = 'Good evening'

Note

We will have a dedicated section for strings in future lessons.

Float

A floating point number is a number that has a decimal point.

1
pi = 3.14
2
e = 2.718281
3
sqrt2 = 1.4142135623730951
4
y = 0.0
5
z = -1.23456789123456789

Note

In Python, floats are usually (but not necessarily) implemented using C double.

None

None represents void, no value, or null.

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x = None
2
y = None

Note

This is mostly used by functions when they don’t return a value.

Boolean

A boolean is a value that can be either True or False. Some values are tested for truthiness or falsiness, using the if statement, while loop, or other control flow statements. By default everything is considered truthy, except for:

• Constants defined to be false: None, False,
• Zero numeric values: 0, 0.0, 0j
• Empty sequences and collections: '', (), [], {}, set(), range(0)

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flag = False
2
isOn = True

Note

Booleans are subtype of integers. Objects are considered falsy if they define the method __bool__ that returns False or __len__ that returns 0. This will be explored in the OOP chapter.

Complex

Complex numbers are numbers that have a real and an imaginary part. Both parts are floating point numbers.

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x = 1.23 + 4.56j
2
y = 1.23 - 4.56j
3
z = 2j
4
t = 1 + 0j
5
u = 0j

Note

The letter j is the imaginary unit, it is defined as the square root of -1. It should exist in a complex number, otherwise it will be treated as a floating point number.