What's the canonical way to check for type in Python?

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What is the best way to check whether a given object is of a given type? How about checking whether the object inherits from a given type?

Let's say I have an object o. How do I check whether it's a str?

Aug 24, 2018 in Python by bug_seeker
• 15,350 points
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1 answer to this question.

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To check if o is an instance of str or any subclass of str, use isinstance (this would be the "canonical" way):

if isinstance(o, str):

To check if the type of o is exactly str:

if type(o) is str:

The following also works, and can be useful in some cases:

if issubclass(type(o), str):

See Built-in Functions in the Python Library Reference for relevant information.

One more note: in this case, if you're using python 2, you may actually want to use:

if isinstance(o, basestring):

because this will also catch Unicode strings (unicode is not a subclass of str; both str and unicode are subclasses of basestring). Note that basestring no longer exists in python 3, where there's a strict separation of strings (str) and binary data (bytes).

Alternatively, isinstance accepts a tuple of classes. This will return True if x is an instance of any subclass of any of (str, unicode):

if isinstance(o, (str, unicode)):

answered Aug 24, 2018 by Priyaj
• 56,520 points

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