'Verify if source file has a valid extension
Args:
source_file (str): The full path of source file or source file.
Returns:
Bool'

def _is_valid_file_ext(self, source_file):

    file_ext = path.splitext(source_file)
    return bool(((len(file_ext) > 1) and (file_ext[(-1)][1:] in self.valid_extensions)))
