How do I enumerate() over a list of tuples in Python?

问题

I've got some code like this:

letters = [('a', 'A'), ('b', 'B')]
i = 0
for (lowercase, uppercase) in letters:
    print "Letter #%d is %s/%s" % (i, lowercase, uppercase)
    i += 1

I've been told that there's an enumerate() function that can take care of the "i" variable for me:

for i, l in enumerate(['a', 'b', 'c']):
    print "%d: %s" % (i, l)

However, I can't figure out how to combine the two: How do I use enumerate when the list in question is made of tuples? Do i have to do this?

letters = [('a', 'A'), ('b', 'B')]
for i, tuple in enumerate(letters):
    (lowercase, uppercase) = tuple
    print "Letter #%d is %s/%s" % (i, lowercase, uppercase)

Or is there a more elegant way?

回答1:

This is a neat way to do it:

letters = [('a', 'A'), ('b', 'B')]
for i, (lowercase, uppercase) in enumerate(letters):
    print "Letter #%d is %s/%s" % (i, lowercase, uppercase)

回答2:

This is how I'd do it:

import itertools

letters = [('a', 'A'), ('b', 'B')]
for i, lower, upper in zip(itertools.count(),*zip(*letters)):
    print "Letter #%d is %s/%s" % (i, lower, upper)

EDIT: unpacking becomes redundant. This is a more compact way, which might work or not depending on your use case:

import itertools

letters = [('a', 'A'), ('b', 'B')]
for i in zip(itertools.count(),*zip(*letters)):
    print "Letter #%d is %s/%s" % i

回答3:

You can do this way too:

letters = [('a', 'A'), ('b', 'B')]
for i, letter in enumerate(letters):
    print "Letter #%d is %s/%s" % (i, letter[0], letter[1])

来源：https://stackoverflow.com/questions/849369/how-do-i-enumerate-over-a-list-of-tuples-in-python

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