title: module 'keras.backend' has no attribute 'tf'
body: <p>While running an old script, after updating keras and tensorflow, I faced the following error:</p>
  <pre><code>    module 'keras.backend' has no attribute 'tensorflow_backend'
  </code></pre>
  <p>For the following line of code</p>
  <pre><code>    print(K.tensorflow_backend._get_available_gpus())
  </code></pre>
  <p>I come to understand that this could be issue of <strong>version mismatches</strong>. The corresponding versions of <strong>Keras</strong> and <strong>Tensorflow</strong> are</p>
  <pre><code>    2.4.3
      2.2.0
      python - 3.7.5
  </code></pre>
  <p>What is the right version compatibiltiy / combination that I should make use of, to overcome this error?</p>