Why plt.imshow() doesn't display the image?

Question

I am a newbie to keras, and when I tried to run my first keras program on my linux, something just didn't go as I wish. Here is my python code:

import numpy as np np.random.seed(123) from keras.models import Sequential from keras.layers import Dense, Dropout, Activation, Flatten from keras.layers import Convolution2D, MaxPooling2D from keras.utils import np_utils from keras.datasets import mnist (X_train,y_train),(X_test,y_test) = mnist.load_data() print X_train.shape from matplotlib import pyplot as plt plt.imshow(X_train[0]) 

The last sentence doesn't display anything. I copied those codes from a tutorial with out any modification. And there is nothing wrong with the backend of matplotlib on my computer. I have tested that through the code below.

import matplotlib.pyplot as plt  data = [[0, 0.25], [0.5, 0.75]]  fig, ax = plt.subplots() im = ax.imshow(data, cmap=plt.get_cmap('hot'), interpolation='nearest',                vmin=0, vmax=1) fig.colorbar(im) plt.show() 

And then I got a image like that:

Moreover, I can get X_train[0] printed and it seems nothing wrong.
So what could be the reason for that? Why the imshow() function in my first code didn't display anything?

Answer 1

The solution was as simple as adding plt.show() at the end of the code snippet:

import numpy as np np.random.seed(123) from keras.models import Sequential from keras.layers import Dense, Dropout, Activation, Flatten from keras.layers import Convolution2D, MaxPooling2D from keras.utils import np_utils from keras.datasets import mnist (X_train,y_train),(X_test,y_test) = mnist.load_data() print X_train.shape from matplotlib import pyplot as plt plt.imshow(X_train[0]) plt.show() 

Answer 2

plt.imshow just finishes drawing a picture instead of printing it. If you want to print the picture, you just need to add plt.show.