How can I pass a tuple to str.format()?

问题

I'm trying to use the str.format() function to print a matrix in columns.

This is the line that goes wrong:

>>>> "{!s:4}{!s:5}".format('j',4,3)
'j   4    '
>>>> "{!s:4}{!s:5}".format(b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: tuple index out of range
>>> b
('dat', 'is')

What am I doing wrong?

Edit: I think I know what the problem is: I'm passing a tuple with two elements, which is than passed on to the function as a tuple with one element, my original tuple. Hence this error. so the question is rather how to pass this tuple to the format function...

回答1:

You can unpack the tuple if you can be certain of its length.

>>> "{!s:4}{!s:5}".format(*b)
'j   4    '

回答2:

EDIT: Sorry I answered your question too soon before I fully understood it. I think you want to unpack the tuple, exactly as in progo's answer.

It depends slightly on what version of Python you're using. The following works for Python 3.5 (and probably all Python 3).

Code:

b = ("dat", "is")
"{0}".format(b)

Output:

"('dat', 'is')"

Also check the Python docs on string formatting.

来源：https://stackoverflow.com/questions/29888630/how-can-i-pass-a-tuple-to-str-format