Question

Probably a silly question, but in python is there a simple way to automatically pad a number with zeros to a fixed length? I wasn’t able to find this in the python docs, but I may not have been looking hard enough? e.i. I want bin(4) to return 00100, rather than just 100. Is there a simple way to ensure the output will be six bits instead of three?

Answer 1

Strings have a .zfill() method to pad it with zeros:

>>> '100'.zfill(5)
'00100'

For binary numbers however, I’d use string formatting:

>>> '{0:05b}'.format(4)
'00100'

The :05b formatting specification formats the number passed in as binary, with 5 digits, zero padded. See the Python format string syntax. I’ve used str.format() here, but the built-in format() function can take the same formatting instruction, minus the {0:..} placeholder syntax:

>>> format(4, '05b')
'00100'

if you find that easier.