variable number of digit in format string

Question

Which is a clean way to write this formatting function:

def percent(value,digits=0):
    return ('{0:.%d%%}' % digits).format(value)

>>> percent(0.1565)
'16%'

>>> percent(0.1565,2)
'15.65%'

the problem is formatting a number with a given number of digits, I don't like to use both '%' operator and format method.

Answer 1

I like this one:

'{0:.{1}%}'.format(value, digits)

Test:

>> '{0:.{1}%}'.format(0.1565, 0)
'16%'
>> '{0:.{1}%}'.format(0.1565, 2)
'15.65%'

Answer 2

From the docs:

Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.

Example:

def percent(value, digits=0):
    print '%.*f%%' % (digits, value*100)
>>> percent(0.1565, 2)
15.65%