How Can I Left-Pad a String or Number with Zeros in Python?

Pad Strings with Zeros

This article addresses the query of how to add zero padding to the left of a numerical string, ensuring a specific length for the string. Two primary methods exist for achieving this: padding strings and padding numbers.

Padding Strings

To pad strings, use the zfill() function:

n = '4'
print(n.zfill(3))  # Outputs "004"

Padding Numbers

For numbers, there are several options:

• f-strings (Python ≥3.6):

n = 4
print(f'{n:03}')  # Recommended, Outputs "004"

• % formatting (Python 2.6 ):

print('%03d' % n)  # Outputs "004"

• format() function (Python 2.6 ):

print(format(n, '03'))  # Outputs "004"
print('{0:03d}'.format(n))  # Outputs "004"
print('{foo:03d}'.format(foo=n))  # Outputs "004"

• format() with curly brackets (Python 2.7 ):

print('{:03d}'.format(n))  # Outputs "004"

Refer to the official String formatting documentation for further information.

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