Difference between list(dict) and dict.keys()?

Question

Say I have a dict:

foo = {'a': 1}

Both list(foo) and foo.keys() return the same thing. What's the difference between the two?

Answer 1

One difference is in Python 3. foo.keys() returns an iterator of the keys, which is what foo.iterkeys() does in Python 2, while list(foo) returns a list of the keys.

As noted below, foo.keys() doesn't exactly return an iterator in Python 3. It returns a dict_keys object (or view) which, among its operations, allows iteration. You can also do fun things such as set operations and multiple iteration. It still has the concept of lazy evaluation which makes iterators so powerful.

Answer 2

Python3:

from the official documentation

Calling foo.keys() will return a dictionary view object. It supports operations like membership test and iteration, but its contents are not independent of the original dictionary – it is only a view.

in fact,

type(foo.keys())

gives

<class 'dict_keys'>

whereas in Python 2 both

type(list(foo))
type(foo.keys())

give

<type 'list'>