Understand variables and dynamic typing

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A variable is a named container that holds a value in your computer's memory. You create a variable in Python by choosing a name and assigning it a value using the assignment operator (=).

Right-to-left rule

When you assign a value to a variable, Python looks at the value on the right side first, and then assigns that value to the named container on the left side.

player_name = "Alex"
player_age = 25
high_score = 98.5

You can update a variable at any time by assigning it a new value:

score = 98.5
score = 100
print(score) # Output: 100

You can try running this code yourself in an online python interpreter at https://aka.ms/python-coder.

Naming variables

Python variable names must follow a few strict rules. Breaking them causes errors in your code:

• Must start with a letter or an underscore (_), never a number (for example, 1st_place is illegal).
• Can only contain letters, numbers, and underscores. No spaces allowed.
• Are case-sensitive (score and Score are two completely separate containers).

By convention, Python developers use snake_case—all lowercase letters with underscores between words:

student_name = "Alex"
final_score = 95

Data types

Every value stored in Python has a data type that tells the computer how to treat it. The three most common types are:

Type Name	Python Label	Description	Example
Integer	int	Whole numbers (positive or negative)	42, -7
Floating Point	float	Decimal numbers	3.14, -0.5
String	str	Text wrapped in quotes	"Hello", "42"

Note

In Python, the int 42 and str "42" are two completely different values. The first is a number you can perform math operations on, while the second is text.

Dynamic typing

In many programming languages, you must explicitly tell the computer what type a variable holds before you can use it. However, Python uses dynamic typing—it figures out the type automatically based on the value you assign.

Because of this behavior, a variable can even change its data type mid-program if you assign it something new:

system_status = 10        # Python automatically sets system_status to an 'int'
system_status = "Active"  # Python dynamically changes system_status to a 'str'

Checking a type

You can check the type of any variable using the built-in type() function:

score = 98.5
print(type(score)) # Output: <class 'float'>