转自：https://keras.io/backend/

At this time, Keras has three backend implementations available: the TensorFlow backend, the Theano backend, and the CNTK backend.

• TensorFlow is an open-source symbolic tensor manipulation framework developed by Google.
• Theano is an open-source symbolic tensor manipulation framework developed by LISA Lab at Université de Montréal.
• CNTK is an open-source toolkit for deep learning developed by Microsoft.

Switching from one backend to another

If you have run Keras at least once, you will find the Keras configuration file at:

$HOME/.keras/keras.json

//HOME对不同的用户可能不同，可以使用echo $HOME查看路径，并且.keras是隐藏文件夹，可以使用ls查看，之后进入编辑模式，直接更改就可以了。