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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 valuePop(ctxt):
 """Pops the top XPath object from the value stack """

    if ctxt is None: ctxt__o = None
    else: ctxt__o = ctxt._o
    ret = libxml2mod.valuePop(ctxt__o)
    return ret