Error in ocropus-econf with some k-options

[zuphilip]

The function ocropus-econf returns an error when comparisons should only be done among the letters or digits, i.e.

$ ocropus-econf -k digits output/*/*.gt.txt
Traceback (most recent call last):
  File "/usr/local/bin/ocropus-econf", line 59, in <module>
    outputs = sorted(list(outputs))
  File "/usr/local/lib/python2.7/dist-packages/ocrolib/common.py", line 560, in parallel_map
    result = fun(e)
  File "/usr/local/bin/ocropus-econf", line 50, in process1
    err,cs = edist.xlevenshtein(txt,gt,context=args.context)
  File "/usr/local/lib/python2.7/dist-packages/ocrolib/edist.py", line 43, in xlevenshtein
    cost = current[n]
UnboundLocalError: local variable 'current' referenced before assignment

[zuphilip]

Okay, it seems that the function xlevenshtein(a,b,context=1) is not yet covering the boundary cases:

1. a="", b="" --> I guess we can simply catch that case in the beginning and output the correct thing, i.e. return 0,[] (I am guessing)
2. a=/="", b="" --> Maybe, the simplest would be to call xlevenshtein(b,a,context=1). Then the cost should be the same and we just have to swap each entry of the confusion matrix list.

Note, these two cases means that the ground truth is empty, which is normally not reasonable to assume. However, if we restrict the comparison for example to digits-only with the k-options, then these cases have to be handled as well.

[zuphilip]

The implementation in hocr-tools looks different and it seems to exactly deal also with these cases: https://github.com/tmbdev/hocr-tools/blob/master/hocr-eval-lines#L36-L57