Variables
Python · Reference cheat sheet
Variables
Python · Reference cheat sheet
📋 Overview
A variable is a name that refers to a value in memory. Python creates the binding when you assign with =. You do not declare types up front (though type hints are optional).
🔧 Core concepts
| Idea | Meaning |
|---|---|
| Assignment | name = value binds a name to an object |
| Rebinding | name = other points the name at a new object |
| Dynamic typing | The same name can later hold a different type |
| Naming | Letters, digits, _; cannot start with a digit |
| Convention | snake_case for variables and functions |
Common built-in types beginners meet first: int, float, str, bool, list, dict, None.
💡 Examples
Create and use variables:
age = 30
name = "Sam"
height_m = 1.75
is_student = True
print(name, age)
print(f"{name} is {age} years old")Rebind and swap:
x = 10
x = x + 5 # now 15
x += 1 # now 16
a, b = 1, 2
a, b = b, a # swap
print(a, b) # 2 1Multiple assignment and unpacking:
city, country = "Lisbon", "Portugal"
first, *rest = [10, 20, 30, 40]
print(first, rest) # 10 [20, 30, 40]Names are references:
nums = [1, 2, 3]
alias = nums
alias.append(4)
print(nums) # [1, 2, 3, 4] — same list object⚠️ Pitfalls
=is assignment;==is comparison.- Using a name before assignment raises
NameError. - Mutable defaults and shared list/dict aliases surprise beginners.
- Avoid names that shadow builtins:
list,str,id,type,input.