C++ "map" in Python

Question

I was wondering if there is a C++ "map"-like thing in Python. For example if I have 10^9 items and each one needs to hold one value: True or False (only the "True"-values are meaningful, but in order to check fast and not in O(n^2)), my code is very inefficient:

for k in range(0, numberOfItems):
myList.append([False])

I can check the value is True or False, but with larger numbers, like 10^9, I get a runtime error because of the list size. It just can't hold that many items. Any help would be appreciated, thanks in advance!

See https://docs.python.org/3/tutorial/datastructures.html#dictionaries — Fred Larson, Dec 21 '17 at 19:08
Although if you can't make a list of 10^9 items, you probably wouldn't be able to create a dict, either. — Barmar, Dec 21 '17 at 19:09
If your problem is slow lookup, use a dictionary: `dct = {}; ... dct[k] = True`, which has O(1). If your problem is memory usage, dictionaries won't help, but neither would C++'s map, which is not memory-efficient. — user4815162342, Dec 21 '17 at 19:09
@Barmar yeah, since this map simply holds a value of true or false, then you could just check membership in a `set` anyways. — juanpa.arrivillaga, Dec 21 '17 at 19:09
yeah, the best solution is probably a `set` that only contains the `True` indexes. — Barmar, Dec 21 '17 at 19:10
@user4815162342 indeed. However, it isn't really look-up that is slow on a list, i.e. `bool_list[i]` is just as fast (probably *faster*) than `bool_map[i]`. It's membership testing that is constant time with a map. — juanpa.arrivillaga, Dec 21 '17 at 19:10

score -2 · Accepted Answer · answered Dec 21 '17 at 19:10

-2

Sure that exist you can use dictionary !
See docs for more informations over how it works : link to python documentation over dictionary

answered Dec 21 '17 at 19:10

Alexandre Jacobs

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3

You should give an example (not shown at first posting this type of question) and not just a referal. Please improve your answer. – ZF007 Jan 01 '18 at 14:34
Thanks for providing an answer. To make sure that answers are always helpful and up to date, link-only answers are discouraged. You can improve your answer buy giving some context around the documentation by showing how to use a dictionary yourself, for example. You can learn more about how to give an answer here: https://stackoverflow.com/help/how-to-answer – stefanobaghino Jan 01 '18 at 14:38

C++ "map" in Python

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