isinstance vs type and == vs is

There are multiple ways in Python to achieve a single task and at times you can get away with implementing things the wrong way and getting the correct answer.

This TIL has come into existence as I struggled with a issue that I was trying to fix at work.

`isinstance` vs `type`

We’ve all used the type and the isinstance method at some point in our functions.

s = 'foo'
if type(s) == str:
    print('this variable is of string type')

if isinstance(s, str):
    print('this variable is of string type')

If you were to execute this code, you would get the same output.

But what’s the difference between them?

instance can check types of even derived classes (meaning, it is intended to be used in cases involving inheritence) whereas type is not.

TLDR; ¹

class Person: pass

class Student(Person): pass


isinstance(Person(), Person)        # returns True
type(Student()) == Student          # returns True
isinstance(Student(), Person)       # returns True
type(Student()) == Person           # returns False, and this probably won't be what you want.

There’s a similar confusion between is and ==.

`is` vs `==`

is looks for the same object (in memory), whereas == looks for the values referred by the variables.

TLDR; ²

n = 5
if n == 5: print('Yep!')    # prints Yep!
if n is 5: print('Yay!')    # prints Yep!

L = []
L.append(1)

if L == [1]: print('Yay!')  # prints Yep!
if L is [1]: print('Yay!')  # prints nothing

H/T to Zach Mueller for helping me understand this

`isinstance` vs `type` and `==` vs `is`