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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 sigint_handler(signum, frame):
 """Exit gracefully on ctrl-C."""

    global _handled_int
    if not _handled_int:
        _handled_int = True
        if not _env_var_true("_REZ_QUIET_ON_SIG"):
            print >> sys.stderr, "Interrupted by user"
        sigbase_handler(signum, frame)