How to switch Backend with Keras (from TensorFlow to Theano)

Question

Create a .keras (note the . in front) folder in you home directory and put the keras.json file there.

For example, /home/DaniPaniz/.keras/keras.json (or ~/.keras/keras.json in short) if you are on a UNIX like system (MacOS X, Linux, *BSD). On Windows you want to create the folder %USERPROFILE%/.keras and put the JSON file there.

Alternatively, you can also set the environment variable KERAS_BACKEND:

KERAS_BACKEND=theano python mymodel.py

In case you want to change the config permanently, the json is available here: ~/.keras/keras.json and you can change the backend.

To do this dynamically in python 2.7 you can run:

from keras import backend as K
import os

def set_keras_backend(backend):

    if K.backend() != backend:
        os.environ['KERAS_BACKEND'] = backend
        reload(K)
        assert K.backend() == backend

set_keras_backend("theano")

I had an issue where I could not from keras import backend at all until I set the backend to theano. The provided answers should work if you can import backend, but if not, just use:

import os
os.environ['KERAS_BACKEND'] = 'theano'
import keras as ks
# Using Theano backend.

In windows, you need to find .keras folder in your C drive. Most probably, it will be somewhere in C:/users/username/. There you will find .keras folder, it contains a json file, keras.json, open it. You will see:

{
“backend”: “tensorflow”,
“floatx”: “float32”,
“epsilon”: 1e-07
}

more or less. replace 'tensorflow' with 'theano'. and save the file.

If you're using windows you can run from command line:

set "KERAS_BACKEND=theano"

from keras import backend as K
from os import environ

# user defined function to change keras backend
def set_keras_backend(backend):
    if K.backend() != backend:
       environ['KERAS_BACKEND'] = backend
       reload(K)
       assert K.backend() == backend

# call the function with "theano"
set_keras_backend("theano")

Type following on command prompt and press enter:

%USERPROFILE%/.keras/keras.json

Change backend in the opened text file and save it. You are done.