Variables & Types

12 min

Explanation

Python variables don't need a declared type — you just assign a value, and Python figures out the type from the value itself. This is called dynamic typing.

x = 5        # x is an int
x = "hello"  # now x is a str — same variable, different type

There's no int x = 5; like in Java or C++. The name x is just a label pointing at whatever object you last assigned to it.

Try it

Run this to see how the same variable name can point at different types over its lifetime.

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Explanation

Python's built-in scalar types you'll use constantly:

int — whole numbers: 5, -12, 1_000_000
float — decimals: 3.14, -0.5
str — text: "hello", 'also fine'
bool — True / False
None — Python's "nothing here" value (like null)

Mixing int and float in an expression (e.g. 5 / 2) automatically produces a float. Integer division uses // instead.

Exercise

Write a function `fahrenheit_to_celsius(f)` that converts a Fahrenheit temperature to Celsius using the formula (f - 32) * 5 / 9, and returns the result.

Exercise

Write a function `swap(a, b)` that returns a tuple `(b, a)` — swap the two values using tuple unpacking, without a temporary variable.

Quiz

What does `type(5.0)` return in Python?

Checkpoint

You can now create variables and reason about Python's dynamic typing.