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The swapcase() string method is used to swap the cases of characters in a string, i.e. from lowercase to uppercase or from uppercase to lowercase.

Note : None of the string methods change the original string and 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 swapcase()

The swapcase() method has no parameters, so we don't have to worry about passing it some value.

# Signature of swapcase() method 
swapcase()

Calling swapcase() method on a string object.




# Python - Method swapcase() Example



# Creating a string
s1 = ('Did you know that Moon is not a planet?')


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


# Calling  the swapcase() method on string object 
print('Calling the swapcases() method  on string : ', s1.swapcase())





Output




Value of string  :  Did you know that Moon is not a planet?
Calling the swapcases() method  on string :  dID YOU KNOW THAT mOON IS NOT A PLANET?


A string object was initialized to a value Did you know that Moon is not a planet?. When the method swapcase() was called on this string object, it returned a string with all its upper case characters changed to lower case and lower case characters changed to upper case.






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


The method swapcase() does not modify the original string, but, it only returns a transformed version of the invoked string by swapping the cases of its characters.


Let's show you this by an example -:
Here in program below, we have initialized a string object with a value MARS - The Red Planet and we are trying to lower case all of its lower case characters by calling the swapcase() method on it.



# Python - Method swapcase() Example



# Creating a string
s1 = ('MERCURY - A planet closest to the Sun')

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


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


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





Output is :




String's value : Jupiter - MERCURY - A planet closest to the Sun
Calling the swapcase() method : mercury - a PLANET CLOSEST TO THE sUN
Original string after calling swapcase() - MERCURY - A planet closest to the Sun


Even after calling the method swapcase() on the string object, the original case of its content remains the same i.e. MERCURY - A planet closest to the Sun, because the method swapcase() only returns a new string by swapping the cases of all of its characters, without changing the original invoked 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 in order to display the impact of calling the swapcase() method on the original object, we can make the reference variable to the original string, point to the result of calling the swapcase() method(but in this case, the original string will be lost).



# Python - swapcase() method example.



# Creating a string
s = 'In Life, Good things don\'t come easy'


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


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


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





Output is :




Original string is :  In Life, good things don't come easy
String value after swapcase()  :  iN lIFE, GOOD THINGS DON'T COME EASY








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