On this page
numpy.core.defchararray.chararray.swapcase
method
chararray.swapcase()[source]- 
    
For each element in
self, return a copy of the string with uppercase characters converted to lowercase and vice versa.See also
char.swapcase 
© 2005–2019 NumPy Developers
Licensed under the 3-clause BSD License.
 https://docs.scipy.org/doc/numpy-1.16.1/reference/generated/numpy.core.defchararray.chararray.swapcase.html