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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 cache_call_signatures(source, user_pos, stmt):
 """This function calculates the cache key."""

    index = user_pos[0] - 1
    lines = source.splitlines() or ['']
    if source and source[-1] == '\n':
        lines.append('')

    before_cursor = lines[index][:user_pos[1]]
    other_lines = lines[stmt.start_pos[0]:index]
    whole = '\n'.join(other_lines + [before_cursor])
    before_bracket = re.match(r'.*\(', whole, re.DOTALL)

    module_path = stmt.get_parent_until().path
    return None if module_path is None else (module_path, before_bracket, stmt.start_pos)