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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 write_pid_file(fn):
 """ Create a file with our PID. """

    if not fn:
        return None
    if fn == '' or fn == "''":
        # work around argument passings in init-scripts
        return None
    f = open(fn, "w")
    f.write("%s\n" % (os.getpid()))
    f.close()