Returns a Boolean stating whether the object is in the container.

A [not] in B

A

Any valid object.

B

Any valid object.

#TODO

O(1) for dict O(n) for sequence (str, list, tuple)

When used with dictionaries checks the keys instead of values.

>>> 'A' in 'ABCD'
True
>>> 0 in [0, 1, 2]
True
>>> 0 not in {'a': 0, 'b': 1}
True

#TODO