Python isinstance() Method

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isinstance() function to determine if an object is a known type, similar to type().

Related course: Complete Python Programming Course & Exercises

syntax

The following is the syntax of the isinstance() method:

isinstance(object, classinfo)

• object -- the instance object.
• classinfo -- can be a direct or indirect class name, a base type or a tuple with them.

Return value Returns True if the object is of the same type as argument two (classinfo), otherwise False.

isinstance example

An example of using the isinstance function is shown below.

>>>a = 2
>>> isinstance (a,int)
True
>>> isinstance (a,str)
False
>>> isinstance (a,(str,int,list)) # is one of the tuple that returns True
True

You can use isinstance in an if statement or function like this:

def trim(a):
    if not isinstance(a,str):
        raise TypeError('argument must be str type')
    if a=='':
        return a

Direct on code.

class BaseC:
    pass

class TestC(BaseC , str):
    pass

# type() does not consider a child class to be a type of the parent class
print(type( TestC()) == BaseC)
print(type( TestC()) == TestC)

# The isinstance() method considers a child class object to be an instance of the parent class
print(isinstance( TestC(),BaseC) )
print(isinstance( TestC(),TestC) )

This works for functions and classes imported from modules too

>>> import datetime
>>> now=datetime.datetime.now()
>>> isinstance(now, datetime.datetime)

type() and isisinstance() functions

type() does not consider a child class to be a kind of parent class

The isinstance() method considers: a child class object to be an instance of the parent class

The program below shows the differences:

>>> isinstance(12, int)
True
>>> type(12)
<class 'int'>

>>> isinstance(3.5, float)
True
>>> type(3.5)
<class 'float'>

>>> isinstance("123 OK",str)
True
>>> type("123 OK")
<class 'str'>