Python String zfill()

In Python to append zeroes on the left side of a string zfill() string method is used. Python string zfill() method is an inbuilt method.

Basically it provides a padding mechanism, where only 0 character is used for padding. The Python center() method is also used for more or less this purpose.

• The zfill() method takes one numeric parameter which help in deciding the number of 0’s to be appended.

• The argument indicates the total required length of the string. So in case the length of the string is less then it is padded with 0 numerals in the left, but if the length of the string is already equal or greater than the length parameter, then no padding is done.

• This function always returns a string.

Suppose we have a string with current length as 30 and length argument passed is 40; then zfill() method will append 10 zeros to the left side of the string and thus make string length equals to 40.

Python String zfill(): Syntax

Below we have a basic syntax of zfill() method in Python:

str.zfill(length)

Note: In the above syntax, str denotes the string variable on which we apply zfill() method.

Python String zfill(): Parameters

The description of parameters of zfill() method is given below:

• length

  This is the only parameter of the zfill() method. This parameter specifies the length of the string that we want to make. This attribute's value must be greater than the actual length of the string, to see any change in the string.

Python String zfill(): Returned Values

It returns a string with the required number of zeroes appended in the main string.

Python String zfill(): Basic Example

Below we have an example to show the working of the zfill() string method in python:

str1="QWERTYUIOP"
str2="STUDYTONIGHT"
str3="no way!!"

print(str1.zfill(20))
print(str2.zfill(5))
print(str3.zfill(4))

The Output will be:

0000000000QWERTYUIOP
STUDYTONIGHT
no way!!

If the passed argument's value or value of length parameter is less than the actual string length then the original string is returned as it is.

Some Points to remember

This method returns the copy of the string with 0's appended to the left-hand side. The length of the string that will be returned is totally dependent upon the length that is passed as a parameter:

1. For example length of the string is 10 and width passed as an argument has value equals to 15. In this situation,the zfill() method returns a string with five zeros appended to its left.

2. Let's take another example with the initial length of the string as 10. The width passed as an argument has value equals to 8. In this case, the string zfill() doesn't fill '0' digits to the left and returns the original string. In this case, the returned string's length will be 10.

Python String zfill(): Another Example

There is another example where input is taken from the user and then zfill() method is applied to it. Let us see the code snippet given below:

for i in range(0,2):
    h=input()
    length=int(input())
    print(h.zfill(length),"\n")

The Output will be:

Hello
6
0Hello

Toy
15
000000000000Toy

Time for Live Example!

Below we have a Live Example of zfill() method. Let us see the code snippet:

Summary

In this tutorial, we learned how to append zero on the left side of a string using zfill() method of strings in Python.