Returns a copy of the string with case swapped.
str. swapcase()
str
#TODO
For 8-bit strings, this method is locale-dependent.
>>> 'foo'
'foo'
>>> 'foo'.swapcase()
'FOO'
>>> 'Foo'.swapcase()
'fOO'
>>> 'fOo'.swapcase()
'FoO'
>>> '123'.swapcase()
'123'
>>> '!@#'.swapcase()
'!@#'
>>> ' '.swapcase()
' '