If only one relationship , nltk.sem.relextract.extract_rels() can't work

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If only one relationship appears in the sentence, nltk.sem.relextract.extract_rels() outputs an empty list. Suggest change relextract.py:

def semi_rel2reldict(pairs, window=5, trace=False):
...
while len(pairs) > 2: # line 184:
reldict = defaultdict(str)
reldict['lcon'] = _join(pairs[0][0][-window:])
reldict['subjclass'] = pairs[0][1].label()
reldict['subjtext'] = _join(pairs[0][1].leaves())
reldict['subjsym'] = list2sym(pairs[0][1].leaves())
reldict['filler'] = _join(pairs[1][0])
reldict['untagged_filler'] = _join(pairs[1][0], untag=True)
reldict['objclass'] = pairs[1][1].label()
reldict['objtext'] = _join(pairs[1][1].leaves())
reldict['objsym'] = list2sym(pairs[1][1].leaves())
reldict['rcon'] = _join(pairs[2][0][:window]) # line 195
...
Suggest :
def semi_rel2reldict(pairs, window=5, trace=False):
...
while len(pairs) >= 2:
reldict = defaultdict(str)
reldict['lcon'] = _join(pairs[0][0][-window:])
reldict['subjclass'] = pairs[0][1].label()
reldict['subjtext'] = _join(pairs[0][1].leaves())
reldict['subjsym'] = list2sym(pairs[0][1].leaves())
reldict['filler'] = _join(pairs[1][0])
reldict['untagged_filler'] = _join(pairs[1][0], untag=True)
reldict['objclass'] = pairs[1][1].label()
reldict['objtext'] = _join(pairs[1][1].leaves())
reldict['objsym'] = list2sym(pairs[1][1].leaves())
reldict['rcon'] = _join(pairs[2][0][:window]) if len(pairs) > 2 else ''
...