Python Data Types

Every value in Python has a type, and that type determines what operations are valid on it and how it behaves. Python's built-in data types cover whole numbers, decimal numbers, text, true/false logic, and the special "no value" marker, along with more advanced numeric and collection types.

Because Python is dynamically typed, you rarely declare types explicitly, but understanding exactly which type a value has is essential for avoiding subtle bugs — especially when mixing numbers and text, or comparing values of different types.

Why it matters

What you are allowed to do with a value depends on its type: you can add two numbers, but adding a number to text is an error. Many beginner bugs come from having a string where a number was expected. Being able to check a type quickly, and knowing the handful of built-in types, lets you read error messages and fix them.

Core Built-in Types

Python provides several fundamental data types that cover the vast majority of everyday programming needs.

• int — whole numbers of arbitrary size, e.g. 42, -7, 1_000_000 (Python ints do not overflow like fixed-size integers in other languages).
• float — decimal (floating-point) numbers, e.g. 3.14, -0.5, 2.0.
• str — text, written in single, double, or triple quotes, e.g. "hello", 'Python'.
• bool — the values True or False, used for logical conditions.
• None — a special singleton value representing "no value" or "nothing here," similar to null in other languages.
• complex — numbers with a real and imaginary part, written like 3+4j, used mainly in scientific computing.

Checking Types at Runtime

Because types are not declared, Python gives you two built-in tools to inspect them. type(value) returns the exact type of a value, which is useful for debugging and quick inspection. isinstance(value, Type) checks whether a value is an instance of a given type (or one of several types passed as a tuple), and is generally preferred in real code because it also correctly recognizes subclasses.

Implicit and Explicit Conversion

Python automatically converts (promotes) an int to a float when the two are combined in an arithmetic expression, such as 3 + 2.0 producing 5.0. Converting between unrelated types — such as text to a number — must be done explicitly using functions like int(), float(), and str(), and will raise a ValueError if the text cannot be interpreted as that type.

Example

age = 25
price = 19.99
name = "Alice"
is_member = True
address = None

print(type(age), type(price), type(name), type(is_member), type(address))
print(isinstance(age, int))
print(isinstance(price, (int, float)))
print(int("42") + 8)
print(str(3.14) + " is pi rounded")

<class 'int'> <class 'float'> <class 'str'> <class 'bool'> <class 'NoneType'>
True
True
50
3.14 is pi rounded

Exercise

Print the name of the type of each value in the list, one per line.

Expected output: int, float, str, bool, NoneType (one per line)

values = [42, 3.14, "hi", True, None]

for value in values:
    # TODO: print the name of the value's type
    pass

values = [42, 3.14, "hi", True, None]

for value in values:
    print(type(value).__name__)

Quick quiz

Interview questions