python 为什么画出来的折线图是这个样子?

if(validation_size):
     validation_accuracy = accuracy.eval(session = sess,feed_dict={x:valiation_images, 
       y_: validation_labels, 
       keep_prob: 1.0})
     print('validation_accuracy => %.4f'%(validation_accuracy))
     plt.plot(x_range, train_accuracies,'-b', label='Training')
     plt.plot(x_range, validation_accuracies,'-g', label='Validation')
     plt.legend() 
     plt.ylabel('accuracy')
     plt.xlabel('step')
     plt.xlim(0,1900)
     plt.ylim(0,1.1)
     plt.show()

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