Use parameter in format string

Question

This:

print '{:x<4d}'.format(34)

prints this:

34xx

How can I do this:

width = 13
print '{:x<|width|d}'.format(34)

to get this:

34xxxxxxxxxxx

Answer 1

You can put one format field inside of the other:

>>> width = 13
>>> print '{:x<{}d}'.format(34, width)
34xxxxxxxxxxx
>>>

From the docs:

A format_spec field can also include nested replacement fields within it. These nested replacement fields can contain only a field name; conversion flags and format specifications are not allowed. The replacement fields within the format_spec are substituted before the format_spec string is interpreted. This allows the formatting of a value to be dynamically specified.

Note however that the nesting can only go one level deep.

Answer 2

This works

('{:x<%dd}' % width).format(34)

Answer 3

this will work:

>>> width = 13 
>>> print '{:x<{}d}'.format(34,width)
34xxxxxxxxxxx

Answer 4

You can nest arguments in format, using kwargs allows you to be more explicit and less susceptible to confusing results:

fillchar = 'x'
width = 13
print "{:{f}<{w}d}".format(34, w=width, f=fillchar)