So I know that "%02d to %02d"%(i, j) in Python will zero pad i and j.
But, I was wondering if there is any way to dynamically zero pad in a format string (I have a list of numbers and I want the zero pad size to be equal to the longest number in that list).
I know that I could use zfill, but I was hoping I could do the entire thing in a format string.
Use the str.format() method of string formatting instead:
'{number:0{width}d}'.format(width=2, number=4)
Demo:
>>> '{number:0{width}d}'.format(width=2, number=4)
'04'
>>> '{number:0{width}d}'.format(width=8, number=4)
'00000004'
The str.format() formatting specification allows for multiple passes, where replacement fields can fill in parameters for formatting specifications.
In the above example, the hard-coded padding width specification would look like:
'{:02d}'.format(4)
or
'{number:02d}'.format(number=4)
with a named parameter. I've simply replaced the 2 width specifier with another replacement field.
To get the same effect with old-style % string formatting you'd need to use the * width character:
'%0*d' % (width, number)
but this can only be used with a tuple of values (dictionary formatting is not supported) and only applies to the field width; other parameters in the formatting do not support dynamic parameters.
number, width = 4, 2, f"{number:0{width}d}" produces '04'.Yes, it's possible
>>> print "%0*d" % (5, 4)
00004
>>> print "%0*d" % (10, 4)
0000000004
