检查部分（类）是否是类的实例的最佳方法

Question

So here's my setup:

from functools import partial

class MyClass:
    def __init__(self, some_kwarg=0):
        pass

def func(class):
    # VERSION 1: I don't do anything

    # VERSION 2: I do this
    class = partial(class, some_kwarg=1)
   
    # check if class points to MyClass
    ### THIS is where I want your input stack overflow

So there are a few things going on here for me:

1. In VERSION 1 should I do class == MyClass ?
2. In VERSION 2 how do I modify the answer to 1 to account for the partial . My naive solution is class.func == MyClass
3. How do I handle cases where I don't know which version it will be? My naive approach is (class == MyClass or (isinstance(class, partial) and partial.func == MyClass))

Answer 1

Firstly, class is a reserved word, so I'll use class_ instead (per PEP8 ).

1. Use is instead of == , to check identity instead of equality (though they'll usually be the same when dealing with class objects).

    class_ is MyClass

   Or, if you need to account for subclasses, use issubclass() , which includes the case where class_ is MyClass .

    issubclass(class_, MyClass)

2. See point 1, just replace class_ with class_.func .

3. You're on the right track. I would just try to flatten out that nested expression, maybe like this:

    departial = class_.func if isinstance(class_, partial) else class_ departial is MyClass

Example:

from functools import partial

class MyClass:
    pass

for class_ in MyClass, partial(MyClass), range, partial(range):
    departial = class_.func if isinstance(class_, partial) else class_
    result = departial is MyClass
    print(result, class_)

Output:

True <class '__main__.MyClass'>
True functools.partial(<class '__main__.MyClass'>)
False <class 'range'>
False functools.partial(<class 'range'>)

Answer 2

MyClass is callable, and returns an instance of MyClass when called.

partial just wraps MyClass in a callable object that, when called, calls MyClass with some predetermined arguments.

partial(MyClass)() , by definition , will return an instance of MyClass . You don't need to check.

(While it's possible to override MyClass.__new__ to return something other than an instance of MyClass , that's not something you would need to check because of partial .)