How to Pad a Numeric String with Zeros to the Left in Python

Using zfill Method

The str.zfill(width) method returns a copy of the string left filled with ASCII '0' digits to make a string of length width. For example,

#!/usr/bin/python3

# s = str(n)
s = '6'
print(s.zfill(4))

# leading sign prefix
s = '-6'
print(s.zfill(4))

0006
-006

Using rjust Method

The str.rjust(width[, fillchar]) method returns the string right justified in a string of length width. For example,

#!/usr/bin/python3

s = '6'
print(s.rjust(4, '0'))

# leading sign prefix
s = '-6'
print(s.rjust(4, '0'))

0006
00-6

Using String Formatting and f-strings

You can use string formatting or f-strings to pad a numeric string with zeros to the left, it really simple. For example,

#!/usr/bin/python3

n = -6

print('%04d' % n)
print(format(n, '04'))
print('{0:04d}'.format(n))
print('{:04d}'.format(n))

# f-strings
# python >= 3.6
print(f'{n:04}')
print(f'{n:0>4}')

-006
-006
-006
-006
-006
00-6