ó ù`]c@ s ddlmZdd„ZdS(iÿÿÿÿ(tdivisioncC sd|dkr|}n|j|ƒs*t‚dt||@ƒt||@ƒtt|ƒt|ƒƒS(sF Return the Alignment Error Rate (AER) of an alignment with respect to a "gold standard" reference alignment. Return an error rate between 0.0 (perfect alignment) and 1.0 (no alignment). >>> from nltk.translate import Alignment >>> ref = Alignment([(0, 0), (1, 1), (2, 2)]) >>> test = Alignment([(0, 0), (1, 2), (2, 1)]) >>> alignment_error_rate(ref, test) # doctest: +ELLIPSIS 0.6666666666666667 :type reference: Alignment :param reference: A gold standard alignment (sure alignments) :type hypothesis: Alignment :param hypothesis: A hypothesis alignment (aka. candidate alignments) :type possible: Alignment or None :param possible: A gold standard reference of possible alignments (defaults to *reference* if None) :rtype: float or None gð?N(tNonetissubsettAssertionErrortlentfloat(t referencet hypothesistpossible((s5lib/python2.7/site-packages/nltk/translate/metrics.pytalignment_error_rate s   !N(t __future__RRR (((s5lib/python2.7/site-packages/nltk/translate/metrics.pyt s