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The zfill() string method is used to strech the length of an invoked string by filling it with a number of zeroes at its beginning.

If the original length of an invoked string is already greater than its length that we want to achieve by adding zeroes to it, then no zeroes are added at the beginning of such invoked string.

Note : None of the string methods change the original string and they only return a new string which reflects the change performed by the string method, hence the returned string must be stored or used(if needed to reflect the result), otherwise it is lost.

• Signature of zfill() method




# Signature of zfill() method 
  
zfill(length)





Parameters	Description
length	This is the length of an invoked string that we want to achieve by filling its beginning with zeroes. It is a non-optional attribute.








• Calling zfill() method on a string object.




# Python - Example of zfill() method



# Creating a string
s1 = ('United Kingdom')


# Printing the original string
print('Value of string  : ', s1)


# Calling  the zfill() method on string object 
print('Calling the zfill() method  on string : ', s1.zfill(20))





Output




Value of string  :  United Kingdom
Calling the zfill() method  on string :  000000United Kingdom


A string object was initialized to a value United Kingdom. When the method zfill() was called on this string object, it returned a string of length 20(greater than the original length of the invoked string), which is filled with a number of zeroes(0) at its beginning.






• Method zfill() does not modify the original characters in a string object


The method zfill() does not modify the original string, but, it only returns a transformed version of the invoked string by filling zeroes at its beginning. Let us show you this by an example.



# Python -Example of zfill() method



# Creating a string
s1 = ('99.76899')

# Printing the original string
print('Original string  before calling zfill() : ', s1)


# Calling  the zfill() method on string object 
# returns a string with zeroes at its beginning, until its length is 20
print('Calling the zfill() method : ', s1.zfill(20))


# Printing the original string
print('Original string after calling zfill() : ',  s1)





Output is :




Original string  before calling zfill() :  99.76899
Calling the zfill() method :  00000000000099.76899
Original string after calling zfill() :  99.76899


As you can see in the example that even after calling the zfill() method on the string object, its original content remains the same i.e. 99.76899, because the method zfill() only returns a transformed version of an invoked string by filling zeroes at its beginning, without changing the original string.




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• Strings are immutable but reference variables are mutable.


String objects are immutable, but the reference variables pointing to them are not, therefore, we can make the reference variable of the original string, point to the new string which is returned after the calling of the zfill() method(but in this case, the original string will be lost).



# Python - zfill() method example.



# Creating a string
s = 'Smile as much as you can!'


# Printing the original string
print('Original string is : ', s)


# Result of calling zfill() is made to reference by the reference of original string.
s = s.zfill(30)


# Old reference variable pointing to the new string
print('String value after zfill() method  : ', s)





Output is :




Original string is :  Smile as much as you can!
String value after zfill() method  :  00000Smile as much as you can!








• A case when an invoked string won't be filled with zeroes.

If the original length of an invoked string is already greater than its length that we want to achieve by adding zeroes to it, then no zeroes are added at its beginning. Let us see an example.

# Python - zfill() method example.



# Creating a string
s = 'Eat healthy, live healthy!'


# Printing the original string
print('Original string is : ', s)



# Finding the length of string by calling len() method
print('length of string : ', len(s))


# Calling  the zfill() method on string object
# by passing its parameter length a value of 10
# which is already less than the length of the invoked string i.e. 26
# Hence, no filling will be made.
print(s.zfill(10))



# Calling  the zfill() method on string object
# by passing its parameter length a value of 20
# which is already less than the length of the invoked string i.e 26
# Hence, no filling will be made.
print(s.zfill(20))




# Calling  the zfill() method on string object
# by passing its parameter length a value of 20
# which is one length greater than the length of the invoked string i.e 26
# Hence, one zero will be added at the beginning of the string' content.
print(s.zfill(27))

Output is :

Original string is :  Eat healthy, live healthy!
length of string :  26
Eat healthy, live healthy!
Eat healthy, live healthy!
0Eat healthy, live healthy!

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