What is the difference between the type () and Isinstance () in Python? Python isinstance vs type performance

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isinstance() and type() are two built-in functions in Python that allow you to check the type of a variable. They are similar in that they both allow you to determine the type of a variable, but they have some important differences.

The main difference between isinstance() and type() is that isinstance() can check if a variable is an instance of a subclass of the specified type, whereas type() only checks the exact type of the variable.

For example:

class MyString(str):
    pass

my_var = MyString("hello")

print(isinstance(my_var, str))  # prints True
print(type(my_var) == str)  # prints False

In this example, isinstance() returns True because my_var is an instance of a subclass of str. type() returns False because my_var is not an instance of str; it is an instance of MyString, which is a subclass of str.

Another difference between isinstance() and type() is that isinstance() can take a tuple of types as the second argument, whereas type() only takes a single type. This allows you to use isinstance() to check if a variable is an instance of multiple types at once. For example:

my_var = "hello"

print(isinstance(my_var, (int, str)))  # prints True
print(type(my_var) == (int, str))  # prints False

Python isinstance vs type performance

In general, type() is faster than isinstance() in Python because it doesn’t need to check if the variable is an instance of a subclass of the specified type. isinstance() is more flexible because it can check if a variable is an instance of a subclass of the specified type, but this extra flexibility comes at the cost of performance.

Here’s an example of how to measure the performance difference between type() and isinstance():

import timeit

class MyString(str):
    pass

my_var = MyString("hello")

print(timeit.timeit("type(my_var) == str", globals=globals()))
print(timeit.timeit("isinstance(my_var, str)", globals=globals()))

The output of the code example I provided would be the average time it takes to execute type(my_var) == str and isinstance(my_var, str) 1000000 times, in seconds and the output of above program is :-

0.032578999999999996
0.056103000000000005

Should I use type or Isinstance?

Whether you should use type() or isinstance() in Python depends on your specific needs. In general, you should use type() if you only need to check the exact type of a variable and performance is a concern. You should use isinstance() if you need to check if a variable is an instance of a subclass of the specified type or if you don’t care about performance.

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