在用plt.subplots画多个子图中，ax = ax.flatten()将ax由n*m的Axes组展平成1*nm的Axes组

以下面的例子说明ax = ax.flatten()的作用：

fig, ax = plt.subplots(nrows=2,ncols=2,sharex='all',sharey='all')
ax = ax.flatten()  for i in range(4):img = image[i].reshape(28, 28)ax[i].imshow(img, cmap='Greys', interpolation='nearest')  # 区别：可以直接用ax[i]

不使用ax = ax.flatten()

fig, ax = plt.subplots(nrows=2,ncols=2,sharex='all',sharey='all') for i in range(4):img = image[i].reshape(28, 28)axs[0, 0].imshow(img, cmap='Greys', interpolation='nearest')  # 区别：不能直接使用ax[i]axs[0, 1].imshow(img, cmap='Greys', interpolation='nearest')axs[1, 0].imshow(img, cmap='Greys', interpolation='nearest')axs[1, 1].imshow(img, cmap='Greys', interpolation='nearest')