Put zeros in front of a number to make it 4 digits [duplicate]

Question

I have a number of four or fewer digits, e.g. 8 or 12 or 197. I'd like to put 0's in front of this number until it is 4 digits long, e.g. 0008 or 0012 or 0197. What would be the easiest way to go about this in Python? What would be the most "Pythonic"?

I could do a series of if statements, like so:

if len(number) == 1:
    number = '000' + number
...

But I have a feeling there is a more elegant way.

Answer 1

Several Pythonic ways to do this, I am really liking the new f-strings as of Python 3.6:

>>> f'{5:04}'
'0005'

This uses the string formatting minilanguage:

>>> five = 5
>>> f'{five:04}'
'0005'

The first zero means the fill, the 4 means to which width:

>>> minimum_width = 4
>>> filler = "0" # could also be just 0
>>> f'{five:{filler}{minimum_width}}'
'0005'

Next using the builtin format function:

>>> format(5, "04")
'0005'
>>> format(55, "04") 
'0055'
>>> format(355, "04")
'0355'

Also, the string format method with the minilanguage:

>>> '{0:04}'.format(5)
'0005'

Again, the specification comes after the :, and the 0 means fill with zeros and the 4 means a width of four.

Finally, the str.zfill method is custom made for this, and probably the fastest way to do it:

>>> str(5).zfill(4)
'0005'