Python String zfill() Method

The String zfill() method returns a new string obtained by padding the string with zeros on the left side to ensure it reaches a specified length width.

This method is particularly useful for formatting numbers or strings to a fixed width, especially when dealing with numeric strings that need to be aligned for display or processing purposes.

Syntax

my_string.zfill(width)

zfill() Parameters

Python String zfill() method parameters:

zfill() Return Value

Python String zfill() method returns a copy of the string with 0 filled to the left.

The length of the returned string depends on the width parameter:

• If width is less than or equal to string length, then the original string is returned.
• If width is greater than string length, then the string with padding is returned.

Examples

Example 1: Zero Padding on the Left of a String with zfill()

This example demonstrates the basic usage of the zfill() method by padding a string with zeros to reach a specified length.

For example, let's pad with zeros to make it 5 characters long:

my_str = "123"
result = my_str.zfill(5)
print(result) # Output: 00123

output

00123

Of course zfill() method works with any type of character (and not only with digits):

my_str = "abc"
result = my_str.zfill(5)
print(result) # Output: 00abc

output

00abc

Example 2: Zero Padding on the Left of a String with Sign Prefix

If the string contains a leading sign + (plus) or - (minus), the zero digits are correctly padded after the sign character.

my_str_positive = "+123"
my_str_negative = "-123"

result_positive = my_str_positive.zfill(5)
result_negative = my_str_negative.zfill(5)

print(result_positive) # Output: +0123
print(result_negative) # Output: -0123

output

+0123
-0123

Example 3: Zero Padding on the Left of a String with smaller width

If the original string is already longer than the specified width parameter, then no padding is added.

For example, let's try to pad a string of length 6 with zeros with width=5:

my_str = "123456"

result = my_str.zfill(5)
print(result) # Output: 123456

output

123456

Equivalent method to Zero Padding on the Left a String

You can obtain the same result of zfill() method by using the format() method.

An example using zfill() method:

my_str = "25"
result = my_str.zfill(6)
print(result) # Output: 000025

output

000025

and equivalent example that uses format() method:

my_str = '25'
result = '{:0>6}'.format(my_str)
print(x) # Output: 000025

output

000025