def get_feature_names(self):
if not isinstance(self.feature_names, list):<EOL><INDENT>raise ValueError(<EOL>'<STR_LIT>')<EOL><DEDENT>else:<EOL><INDENT>return self.feature_names<EOL><DEDENT>
Returns the names of all transformed / added columns.

Returns
-------
feature_names: list
    A list with all feature names transformed or added.
    Note: potentially dropped features are not included!