def alter_file(line_number, input_file_list, implementation, input_path):
"""
Changes source file, when valid implementation found.
:param line_number: of source.
:param input_file_list: contains all lines of source.
:param implementation: the new function.
:param input_path: source file path.
:return: void
"""
source = h.get_function_code(line_number, input_file_list)
input_file_list = input_file_list[:line_number] + implementation + input_file_list[line_number + len(source):]
h.rewrite_file(input_path, input_file_list)