Python String zfill() Function

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.

note

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

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() function parameters:

Parameter	Condition	Description
width	Required	The length of the string with zeros padded to the left

zfill() Return Value

Python String zfill() function 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

warning

The leading + (plus) or - sign is counted as a character in the string!

my_str = "+123"

print(my_str.zfill(4)) # Output: +123
print(my_str.zfill(5)) # Output: +0123

output

+123
+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