Python 3 - using tuples in str.format()

Question

I'm trying to use the str.format() method, and having some difficulties when my values are stored within a tuple. For example, if I do:

s = "x{}y{}z{}"
s.format(1,2,3)

Then I get 'x1y2z3' - no problem.
However, when I try:

s = "x{}y{}z{}"
tup = (1,2,3)
s.format(tup)

I get

IndexError: tuple index out of range.

So how can I 'convert' the tuple into separate variables? or any other workaround ideas?

You are actually passing a single argument that is a `tuple`. — Vishnu Upadhyay, Nov 05 '14 at 13:26
def fun(*args): print('My args: {!a}'.format(args)) I just don't know yet what 'a' means, but it seems to be a 'conversion specifier'. I've also seen the use of 'r'. — eltbus, Oct 20 '19 at 16:17

score 31 · Accepted Answer · edited May 23 '17 at 12:01

31

s = "x{}y{}z{}"
tup = (1,2,3)
s.format(*tup)

The * before tup tells Python to unpack the tuple into separate arguments, as if you called s.format(tup[0], tup[1], tup[2]) instead.

Or you can index the first positional argument:

s = "x{0[0]}y{0[1]}z{0[2]}"
tup = (1,2,3)
s.format(tup)

Demo:

>>> tup = (1,2,3)
>>> s = "x{}y{}z{}"
>>> s.format(*tup)
'x1y2z3'
>>> s = "x{0[0]}y{0[1]}z{0[2]}"
>>> s.format(tup)
'x1y2z3'

edited May 23 '17 at 12:01

Community

answered Nov 05 '14 at 13:25

Martijn Pieters

Thanks! it worked, but can you explain more what's actually going on with the *? or refer me to the right place in the documentation? – soungalo Nov 05 '14 at 13:29
@soungalo: see [What does \*\* (double star) and \* (star) do for Python parameters?](http://stackoverflow.com/q/36901) – Martijn Pieters Nov 05 '14 at 13:30
This really helpful if used inside map() and you don't want to define lambda or custom function to use `*` to unpack the tuple! This is the only solution (that I could find) that talks about indexing in format to unpack tuple. Cheers! – Tim Nov 13 '20 at 17:54

score -3 · Answer 2 · answered Nov 05 '14 at 13:30

-3

You can unpack the contants of the tuple.

s=s.format(*t)

answered Nov 05 '14 at 13:30

user93

1

This doesn't seem to add anything not already covered in an existing answer. – Kevin Nov 05 '14 at 13:34
@Kevin - So downvote it. Don't flag it. – ArtOfWarfare Nov 05 '14 at 14:24
shorter is better – Sean Oct 20 '18 at 15:57

2 Answers2