ظهور الخطأ التالي TypeError: cannot perform reduce with flexible type في بايثون

في مكتبة sklearn حاولت استخدام Gaussian Naive Bayes Module:

training = GaussianNB()
training = training.fit(trainData, target)
prediction = training.predict(testData)

والبيانات كانت:

[['-214' '-153' '-58' ..., '36' '191' '-37']
['-139' '-73' '-1' ..., '11' '76' '-14']
['-76' '-49' '-307' ..., '41' '228' '-41']
..., 
['-32' '-49' '49' ..., '-26' '133' '-32']
['-124' '-79' '-37' ..., '39' '298' '-3']
['-135' '-186' '-70' ..., '-12' '790' '-10']]

ظهر لدي الخطأ التالي :

Traceback (most recent call last):
File "prediction.py", line 90, in <module>
  gaussianNaiveBayes()
File "prediction.py", line 76, in gaussianNaiveBayes
  training = training.fit(trainData, target)
File "/Library/Python/2.7/site-packages/sklearn/naive_bayes.py", line 163, in fit
  self.theta_[i, :] = np.mean(Xi, axis=0)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/ core/fromnumeric.py", line 2716, in mean
  out=out, keepdims=keepdims)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/core/_methods.py", line 62, in _mean
  ret = um.add.reduce(arr, axis=axis, dtype=dtype, out=out, keepdims=keepdims)
TypeError: cannot perform reduce with flexible type

ما المشكلة؟