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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def folder(self) -> typing.Union[str, None]: """ The folder, relative to the project source_directory, where the file resides :return: """


        if 'folder' in self.data:
            return self.data.get('folder')
        elif self.project_folder:
            if callable(self.project_folder):
                return self.project_folder()
            else:
                return self.project_folder
        return None