How do I format a number with a variable number of digits in Python?

Question

Say I wanted to display the number 123 with a variable number of padded zeroes on the front.

For example, if I wanted to display it in 5 digits I would have digits = 5 giving me:

00123 

If I wanted to display it in 6 digits I would have digits = 6 giving:

000123 

How would I do this in Python?

Answer 1

If you are using it in a formatted string with the format() method which is preferred over the older style ''% formatting

>>> 'One hundred and twenty three with three leading zeros {0:06}.'.format(123) 'One hundred and twenty three with three leading zeros 000123.' 

See
http://docs.python.org/library/stdtypes.html#str.format
http://docs.python.org/library/string.html#formatstrings

Here is an example with variable width

>>> '{num:0{width}}'.format(num=123, width=6) '000123' 

You can even specify the fill char as a variable

>>> '{num:{fill}{width}}'.format(num=123, fill='0', width=6) '000123' 

Answer 2

There is a string method called zfill:

>>> '12344'.zfill(10) 0000012344 

It will pad the left side of the string with zeros to make the string length N (10 in this case).