CODEWITHSUNDEEP
pythonpython-2.7typesset
Tom
Tom

Reputation: 3336

What is the type of set() in Python?

a = ['a', 'b', 'c', 'd']
b = set(a)
print isinstance(a, types.ListType)
print isinstance(b, types.ListType)

The result shows that b is not of types.ListType. However, there is no 'SetType' in Python. So what is the type 'XXXType' so that isinstance(b, types.XXXType) is True?

Upvotes: 4

Views: 5912

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1121446

Use isinstance(b, set).

The types references to built-in types are just there for convenience* and are otherwise deprecated (they have been removed from the Python 3.x version of the types module). As such set was never added.

For example, types.ListType is just an alias for list:

>>> import types
>>> types.ListType is list
True
>>> isinstance([1, 2, 3], list)
True

If you must have a SetType reference in the types module, simply add the alias yourself:

types.SetType = set

If you are looking for an abstract base class for the basic container type, use the collections module ABCs; these signal what methods a type support and checking against these types can let you detect a wider set of types that support specific operations (rather than be an instance of just the list and set types):

>>> from collections import Set, MutableSequence
>>> isinstance([1, 2, 3], MutableSequence)
True
>>> isinstance({1, 2, 3}, Set)
True

* History lesson: Once upon a time, the built-in types like int and list were not really classes, and the built-in names int() and list() were simply functions to convert to the built-in types. That means that the names were simply not the same object as types.IntType and types.ListType and you had to use the types module to be able to use isinstance() on a list object. That time is now long, long behind us, and the role of the types module has changed.

Upvotes: 13

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