如何使用fromiter构造一个np.array

import numpy as np
data = np.eye(9)
labels = np.array([0,1,2,2])

def extract_one_class(X,labels,y):
""" Take an array of data X,a column vector array of labels,and one particular label y.  Return an array of all instances in X that have label y """

    return X[np.nonzero(labels[:] == y)[0],:]

def generate_points(data,size):
""" Generate and return 'size' pairs of points drawn from different classes """

     label_alphabet = np.unique(labels)
     assert(label_alphabet.size > 1)

     for useless in xrange(size):
         shuffle(label_alphabet)
         first_class = extract_one_class(data,label_alphabet[0])
         second_class = extract_one_class(data,label_alphabet[1])
         pair = np.hstack((first_class[randint(0,first_class.shape[0]),:],second_class[randint(0,second_class.shape[0]),:]))
         yield pair

points = np.fromiter(generate_points(data,5),dtype = np.dtype('f8',(2*data.shape[1],1)))

extract_one_class函数返回数据子集：属于一个类标签的所有数据点.我想要得到一个带有shape =(size,data.shape [1])的np.array.目前,上面的代码段会返回错误：

ValueError: setting an array element with a sequence.

fromiter的文档声称返回一维数组.还有一些人曾经使用过fromiter来构建numpy中的记录数组(例如http://iam.al/post/21116450281/numpy-is-my-homeboy).

假设我能以这种方式生成数组,那么我是不是很明显？或者我的numpy不太正确？