Levon Levon - 1 month ago 25
Python Question

Using .format() to format a list with field width arguments

I recently (finally?) started to use

.format()
and
have a perhaps a bit obscure question about it.

Given

res = ['Irene Adler', 35, 24.798]


and

(1) print('{0[0]:10s} {0[1]:5d} {0[2]:.2f}'.format(res))
(2) print('{:{}s} {:{}d} {:{}f}'.format(res[0], 10, res[1], 5, res[2], .2))


work great and both print:

Irene Adler 35 24.80
Irene Adler 35 24.80


I didn't know that I could deal with lists as in (1) which is neat. I
had seen about field width arguments (2) with the old
%
formatting before.

My question is about wanting to do something like this which combines (1) and (2):

(3) print('{0[0]:{}s} {0[1]:{}d} {0[2]:{}f}'.format(res, 10, 5, .2))


However, I am unable to do this, and I haven't been able to figure out
from the documentation if this even possible. It would be nice to just
supply the list to be printed, and the arguments for width.

By the way, I also tried this (w/o luck):

args = (10, 5, .2)
(4) print('{0[0]:{}s} {0[1]:{}d} {0[2]:{}f}'.format(res, args))


In both instances I got:

D:\Users\blabla\Desktop>python tmp.py
Traceback (most recent call last):
File "tmp.py", line 27, in <module>
print('{0[0]:{}s} {0[1]:{}d} {0[2]:{}f}'.format(res, 10, 5, .2))
ValueError: cannot switch from manual field specification to automatic field numbering

D:\Users\blabla\Desktop>python tmp.py
Traceback (most recent call last):
File "tmp.py", line 35, in <module>
print('{0[0]:{}s} {0[1]:{}d} {0[2]:{}f}'.format(res, args))
ValueError: cannot switch from manual field specification to automatic field numbering


I also tried using
zip()
to combine the two sequences without luck.

My question is:

Can I specify a list to be printed effectively doing what I was trying
to unsuccessfully do in (3) and (4) (clearly if this is possible, I'm
not using the right syntax) and if so, how?

Answer

The error message

ValueError: cannot switch from manual field specification to automatic field numbering

pretty much says it all: You need to give explicit field indices everwhere, and

print('{0[0]:{1}s} {0[1]:{2}d} {0[2]:{3}f}'.format(res, 10, 5, .2))

works fine.

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