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I would've expected Python's keys method to return a set instead of a list. Since it most closely resembles the kind of guarantees that keys of a hashmap would give. Specifically, they are unique and not sorted, like a set. However, this method returns a list:
>>> d = {} >>> d.keys().__class__ <type 'list'> Is this just a mistake in the Python API or is there some other reason I am missing?
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In Python, the keys() and items() methods of dictionaries dict can be used to perform set operations on keys and key-value pairs. For example, you can generate a dictionary consisting of elements (keys and values) common to multiple dictionaries.
Python Dictionary keys() Method The keys() method returns a view object. The view object contains the keys of the dictionary, as a list. The view object will reflect any changes done to the dictionary, see example below.
Python Dictionary keys() The keys() method extracts the keys of the dictionary and returns the list of keys as a view object.
Python Dictionary keys() The dict. keys() method returns a dictionary view object that contains the list of keys of the dictionary.
One reason is that dict.keys() predates the introduction of sets into the language.
Note that the return type of dict.keys() has changed in Python 3: the function now returns a "set-like" view rather than a list.
For set-like views, all of the operations defined for the abstract base class
collections.abc.Setare available (for example,==,<, or^).
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