Apply autopep8 to the diff lines of a file.

        - Returns the diff between original and fixed file.
        - If self.in_place then this writes the the fixed code the file_name.
        - Prints dots to show progress depending on options.

def fix_file(self, file_name):
        """Apply autopep8 to the diff lines of a file.

        - Returns the diff between original and fixed file.
        - If self.in_place then this writes the the fixed code the file_name.
        - Prints dots to show progress depending on options.

        """
        # We hope that a CalledProcessError would have already raised
        # during the init if it were going to raise here.
        modified_lines = self.modified_lines(file_name)

        return fix_file(file_name, modified_lines, self.options,
                        in_place=self.in_place, diff=True,
                        verbose=self.verbose, cwd=self.cwd)