无法pickle Scikit学习最近邻分类器-无法pickil instancemethod对象

我正在尝试pickle NearestNeighbor模型,但它说无法pickle instancemethod对象。

代码:

import cPickle as pickle
from sklearn.neighbors import NearestNeighbors

nbrs = NearestNeighbors(n_neighbors=50, algorithm='ball_tree', metric=self.distanceCIE2000_classifier)
nbrs.fit(allValues)
with open('/home/ubuntu/nbrs.p','wb') as f:
       pickle.dump(nbrs, f)

完整的回溯:

  File "/home/ubuntu/colorSetter.py", line 82, in createClassifier
    pickle.dump(nbrs, f)
  File "/usr/lib/python2.7/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
  TypeError: can't pickle instancemethod objects