NCD distance raises KeyError when calculating the distance between a sequence and itself

[necrosovereign]

Distance.pairwise_distance from alfpy.ncd raises KeyError when seq1idx == seq2idx.

Example:

import alfpy.ncd as ncd
from alfpy.utils import seqrecords

seq_records = seqrecords.SeqRecords(id_list=[0], seq_list=["ACGT"]
dist = ncd.Distance(seq_records)
print(dist.pairwise_distance(0, 0))

This raises:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "../alfpy/ncd.py", line 67, in pairwise_distance
    zxy = self._complexity[(seq1idx, seq2idx)]
KeyError: (0, 0)