Variables

A variable is a named container that stores a piece of data your program can work with and change while it runs. In Python, you never declare a type for a variable — the general pattern is simply name = value, and Python figures out what kind of data it is automatically. This is called dynamic typing: a variable's type is determined by whatever value it currently holds, and that can even change later if you assign it something new.

age = 25
print(age)

Variable names in Python must start with a letter or an underscore (_) — never a digit — and can't be one of Python's reserved keywords (like if or class). Names are case-sensitive, so score and Score are two different variables. By convention, Python developers write variable names in snake_case: all lowercase, with underscores separating words, e.g. total_score or first_name.

Python's naming convention for variables is ____, where words are lowercase and separated by underscores, such as total_score.

A variable can also be reassigned: given a new value after it already has one. The new value simply replaces the old one, and unlike statically typed languages, the new value does not even need to be the same type as before — a variable that held a number can later hold text.

lives = 3
lives = lives - 1
print(lives)  # 2

lives = "game over"
print(lives)  # now a string, and that's fine

Python also lets you assign several variables at once on a single line by separating both the names and the values with commas. This is called multiple assignment, and it is a common, tidy way to set up related variables together.

a, b = 1, 2
print(a)  # 1
print(b)  # 2

name, age, is_student = "Maya", 21, True

What happens when you reassign a Python variable to a value of a different type than it held before?

In Python, you must write a type keyword before a variable name when creating it, similar to int in other languages.