Python: using .format method to populate string with list items

Question

This seems like a question that should already have an answer, but I didn't find one. If anyone knows of another question that has already answered this, please post a comment with the link.

My question is, is there a way to input the items from a list into a string using the .format method? Using specific indices to format is kind of a pain, I am wondering if it is possible to use a "for i in list" technique.

So rather than this:

 x = [1, 2, 3, 4, 5]

print 'The first 4 items in my list are {}, {}, {}, {}'.format([x[0], x[1], x[2], x[3])

I could do something like:

x = [1, 2, 3, 4, 5]

print 'The first 4 items in my list are {}, {}, {}, {}'.format([i for i in x if i < 5])

if I try something along these lines, it won't work and I will get a "tuple index out of range" error, because it sees this as only 1 item rather than 4 separate items. I'm just wondering if this is possible.

user2555451 · Accepted Answer · 2015-03-13 20:29:28Z

7

You can simply unpack the list:

>>> x = [1, 2, 3, 4, 5]
>>> 'The first 4 items in my list are {}, {}, {}, {}'.format(*x)
'The first 4 items in my list are 1, 2, 3, 4'
>>>

Any remaining arguments will be ignored.

answered Mar 13, 2015 at 20:29

user2555451

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jedwards · Accepted Answer · 2015-03-13 20:33:35Z

0

You could use string.join() on your list comprehension

x = [1, 2, 3, 4, 5]

print 'The first 4 items in my list are {}'.format(', '.join([str(i) for i in x if i < 4]))
# The first 4 items in my list are 1, 2, 3

Note: This only prints three elements, since only 3 elements in x match < 4

If your list comprehension was just an attempt to output only 4 elements, and you're not really interested in using list comprehensions otherwise, iCodez's solution is better and more efficient.

answered Mar 13, 2015 at 20:33

jedwards

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Comments

user11650788 · Accepted Answer · 2020-06-01 17:40:51Z

0

rev_arr = [4,3,2,1]
str_arr.format(', '.join([str(element) for element in rev_arr]))

I want that it should give an ouput like this 4 3 2 1 but its returning an empty string . I am not able to understand why its returning an empty string. I am newbie please elaborate the second line of the snippet to me

answered Jun 1, 2020 at 17:40

user11650788

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