Literals and Variables

In Python, literals represent fixed values like 'Hello, World!' or numbers such as 1 and 2.0. A literal is a direct representation of a constant value in your code. Variables, on the other hand, are used to store these values. You can think of variables as labeled containers that hold data, allowing you to reference and manipulate that data later.

Defining Variables

In Python, variables are defined using the assignment operator =. Here’s how you can assign values to variables:

>>> x = 1
>>> print(x)
1

>>> y = 'a string'
>>> print(y)
a string

>>> foo_bar = 123.456
>>> print(foo_bar)
123.456

The Assignment Operator =

The = operator is used for two main purposes:

  1. Defining a new variable
  2. Updating an existing variable

For example:

>>> x = 1       # Define a new variable
>>> x = x + 1   # Update the existing variable by adding 1 to its value
>>> print(x)
2

Right-to-Left Evaluation

The assignment operator evaluates expressions from right to left. This means the expression on the right of = is evaluated first, and the result is assigned to the variable on the left.

Basic Data Types and the type() Function

Python offers several basic data types to represent different kinds of data. Some of the most common types include:

  • Integer (int)
  • Float (float)
  • String (str)
  • Boolean (bool)

You can use the type() function to check the type of any object in Python.

Integer (int)

Integers are whole numbers, either positive or negative. Here’s an example:

>>> print(1)
1

>>> type(1)
<class 'int'>

Float (float)

Floats are numbers that contain decimal points, representing real numbers. Both 1.0 and 1. are valid float literals in Python:

>>> print(1.0)
1.0

>>> type(1.0)
<class 'float'>

>>> print(1.)
1.0

In Python, 1. and 1.0 are equivalent and represent the same float value.

String (str)

Strings are sequences of characters, enclosed within single quotes ' ' or double quotes " ":

>>> print('one')
one

>>> type("one")
<class 'str'>

Boolean (bool)

Booleans represent truth values and can only have two possible outcomes: True or False. Note that in Python, these values are case-sensitive. Lowercase true and false are not recognized as valid boolean values.

>>> print(True)
True

>>> type(False)
<class 'bool'>

Comments in Python

Comments are lines of code that the Python interpreter ignores. Comments help make your code easier to understand, but they don’t affect how the program runs. In Python, a comment starts with the # symbol.

Single-Line Comments

>>> # This is a comment
>>> # print(1)

Since the second line is a comment, the statement print(1) is not executed, and no output is produced.

Inline Comments

You can also add comments at the end of a line of code:

>>> print(1)  # This line prints the number 1
1