Values and Types

Why this matters

Python treats a number, a piece of text and a yes/no answer very differently. Knowing which type of value you have explains most surprising behaviour, and most TypeErrors.

The idea

Every value has a type. The four you will use constantly:

Type	What it holds	Examples
int	whole numbers	7, -3, 0
float	numbers with a decimal point	2.5, -0.1, 3.0
str	text (a “string”), written in quotes	"hello", 'Python', ""
bool	yes or no	True, False

Notice that 3 and 3.0 are different types, and "3" (text) is a third thing again. Text in quotes is always a str, even if it looks like a number.

The built-in type() function tells you what you have:

print(type(42))        # <class 'int'>
print(type(2.5))       # <class 'float'>
print(type("42"))      # <class 'str'>
print(type(True))      # <class 'bool'>

A variable has no type of its own; it just holds a value, and that value has one:

x = 5        # x holds an int
x = "five"   # now x holds a str

Try it

Use print(type(...)) on a few things: a whole number, a decimal, "7" in quotes, 7 / 2, True. Predict each answer before pressing Run. What type is 7 / 2?

Your turn

In the editor, each variable currently holds ... (a placeholder). Replace each ... with a value of the type its comment asks for. Then, at the bottom, print the type of the value 42.

Recap

• Every value has a type: int, float, str or bool (and more to come).
• Quotes make text: "7" is a str, 7 is an int.
• type(value) tells you the type.

Common mistakes

• Putting quotes around True. "True" is text; True is a bool.
• Lowercase true. Python only recognises True and False.
• Mixing up 3 and "3". They look similar but behave differently, as you will see when you use +.