Currently, I have Keras with TensorFlow and CUDA at the backend. But, I want to force Keras to use the CPU, at times. So here my question is, whether it can be done on a virtual environment without installing a separate CPU-only TensorFlow. If yes, I would like to know how? I have heard that the flags could be set if Theano is at the backend. But, I have no idea if TensorFlow flags are accessible via Keras.