How to properly check object types in Python?

Problem: I have to check that the a returned value is a Python dictionary.

Q1. Which of these options is the proper way to do this?

type(x) == dict

type(x) == type(dict)

isinstanc开发者_JAVA百科e(d, dict)

Then there are the other variants using is operator instead of ==.

Q2. Many people say that checking the type of an object is generally a bad practice, but regarding to my initial problem, do I have any other choice?

Q1. Which of these options is the proper way to do this?

Don't waste time on type checking.

It's error-prone because it's based on assumptions.

Q2. ... do I have any other choice?

Yes do this.

try:
    x.the_dict_operation()
except TypeError:
    # x was not the expected type for the operation
    raise # or whatever.

In most cases, this amounts to "do nothing".

Just write the code. If "somehow" a malicious sociopath uses the wrong type, it will just crash like it's supposed to.

Rely on behaviour, not on actual type (see other answers).

Lot of objects can act like dictionaries, you don't want to force users of your function/API to use plain dicts, right?

On the pragmatic side:

>>> type({})
<type 'dict'>
>>> dict
<type 'dict'>
>>> type(dict)
<type 'type'>
>>> isinstance({}, dict)
True
>>> isinstance("", dict)
False

Check for __getitem__ rather than verifying the type. If you really want to type-check, any is fine (well, except type(x) == type(dict), that will never be true for a dict instance). isinstance is probably the most standard way to do it.