The built-in isinstance() function checks if an object is an instance of a specified class or a subclass thereof, returning a Boolean value. It’s a versatile tool for explicit type checking in Python, as it considers subclass relationships:
>>> isinstance(42, int)
True
isinstance() Signature
isinstance(object, classinfo)
object The object to check. classinfo A class, tuple of classes, or union type to check against. Return Value
True if the object is an instance of classinfo or a subclass thereof.False if the object isn’t an instance of classinfo.isinstance() Examples
With a number and class as arguments:
>>> isinstance(3.14, float)
True
>>> isinstance(3.14, int)
False
With a number and a tuple of classes as arguments:
>>> isinstance(42, (int, float))
True
With a union type as an argument:
>>> isinstance(42.0, int | float)
True
isinstance() Common Use Cases
The most common use cases for the isinstance() function include:
isinstance() Real-World Example
Say you’re implementing a function that processes different types of numerical data. You can use isinstance() to ensure the input is of a valid type:
>>> def process_number(number):
... if isinstance(number, (int, float)):
... return number ** 2
... else:
... raise TypeError("the input must be an int or float")
>>> process_number(4)
16
>>> process_number(4.5)
20.25
>>> process_number("4")
Traceback (most recent call last):
...
TypeError: the input must be an int or float
In this example, isinstance() ensures that the function processes only integers and floats, and raises a TypeError otherwise.
For additional information on related topics, take a look at the following resources:
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