Python Variables

A variable is a name bound to a value. Python decides the type at runtime — you don't declare it.

Assigning

name   = 'Ada'         # str
age    = 36            # int
active = True          # bool
ratio  = 0.382         # float

Re-assigning changes the type

x = 1
x = 'hello'    # legal; x was an int, now it's a str
x = [1, 2, 3]  # now a list

Multiple assignment

x = y = z = 0          # all three bound to 0
a, b = 1, 2            # tuple unpacking
a, b = b, a            # swap — no temp variable

Naming rules

• Letters, digits, underscores. Can't start with a digit.
• Case-sensitive — age and Age are different.
• Don't shadow built-ins: avoid list, dict, str, id, type as variable names.

Variables hold references

Assigning a list to a second name doesn't copy it. Both names point at the same object:

a = [1, 2, 3]
b = a
b.append(4)
print(a)   # [1, 2, 3, 4] — a saw the change

Example

name = 'Ada'
age = 36
active = True
print(f'{name} is {age} and active={active}')

Exercise

Test yourself