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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 trace(fout=None, format=None, byteorder=sys.byteorder, nanosecond=False):
 """Trace TCP flows. Keyword arguments: * fout -- str, output path * format -- str, output format * byteorder -- str, output file byte order * nanosecond -- bool, output nanosecond-resolution file flag """

    str_check(fout or '', format or '')
    return TraceFlow(fout=fout, format=format, byteorder=byteorder, nanosecond=nanosecond)