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Tobias Edwards
14,458 PointsCan someone please explain 'enumerate' to me, please?
I have come across so many definitions of 'enumerate', but I still don't understand.
Could someone please explain 'enumerate' to me in "Layman's" terms please. This is definitely the hardest part of Python for me to understand thus far.
I would appreciate examples, and when to use it.
Thank you :)
2 Answers
Chris Freeman
Treehouse Moderator 68,423 PointsTo loop over all the items in a list you can simply use the format:
for item in my_list:
# do something with item
But what if you wanted to also utilize the index of an item, you might use:
for idx in range(len(my_list)):
# print each item with it's index
print("{0}. {1}".format(idx, my_list[idx]))
enumerate() provides a way to simplify code for this very common case.
for idx, item in enumerate(my_list):
# print each item with it's index
print("{0}. {1}".format(idx, item))
So for each item in the iterable (such as my_list, or characters in a string, etc), enumerate return a tuple of the o-based count and an item. In the example above, this tuple is unpacked into the variables idx and item.
enumerate-like behavior could be done using:
for idx, item in zip(range(len(my_list)), my_list):
# same as using enumerate but MUCH less readable
rdaniels
27,258 PointsThe enumerate function lets you iterate over the index-value pairs, where the indices are supplied automatically. eg: enumerate(iterable) will iterate over (index, item) pairs, for all items in iterable.... source: Beginning Python
Tobias Edwards
14,458 PointsThanks but I've read that before. Could you give examples and uses, please?
Tobias Edwards
14,458 PointsTobias Edwards
14,458 PointsWow! Thank you sooooo much :)
But, just a small thing: when you format variables in using
print("{0}. {1}".format(idx, my_list[idx]))Why is it you use a '0' and a '1' in the curly braces? I'm only ever used to seeing empty curly braces, sorry
Chris Freeman
Treehouse Moderator 68,423 PointsChris Freeman
Treehouse Moderator 68,423 PointsChanging from empty
{}to numbered{0}specifies the order to apply the positional arguments given toformat(). In the code above, adding the numbers doesn't change anything. Just my preferred style.One application would be if you needed to use an argument twice:
print("{0} {0} {1}!".format("hip", "hooray"))To get
hip hip hooray!Expanding lists as format argument doesn't alway arrive in the desired order. Given the list:
lst = ['Tobias', 'Edwards']How could I print "last_name, first_name"? Let's use numbered format fields:
print("{1}, {0}".format(*lst))Yeilds
Edwards, TobiasTobias Edwards
14,458 PointsTobias Edwards
14,458 PointsChris, you the man! Thank you so much!