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Python Python Collections (Retired) Dictionaries Membership

Posted by Beth Singley
Beth Singley
3,491 Points

how do you check to see if a dict key exists?

Working on matching items in a list against keys in a dict. Within the for loop of the list, I want to test each item to see if it exists as a key. However, this bit of code hangs up every time. 

    item == my_dict[item]

How do you check to see if the item exists as a dict key?

1 Answer

carlin aylsworth
carlin aylsworth
5,650 Points

I would use:

if item in my_dict:
    do_something()

Hope that Helps!

Chris Freeman
Chris Freeman
Treehouse Moderator 68,454 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,454 Points

As Carlin said, this is the typical way to see if a key is present. Keep in mind that this is short hand for:

if item in my_dict.keys():
    do_something()

When a dictionary is used in an iterable context, it's keys are returned. For example:

len(my_dict) is counting the number of keys.