Error when exporting translator in Jupyter Notebook

The notebook "Transformer model for language understanding" works fine on Jupyter Notebook (WSL2 Ubuntu 18.04, Python 3.7) apart for a few warnings until the model has to be exported.

Here the following error obtains:

OperatorNotAllowedInGraphError: Iterating over a symbolic tf.Tensor is not allowed: AutoGraph did convert this function. This might indicate you are trying to use an unsupported feature.

in relation to

for i in tf.range(max_length)

in Translator class.

If I rplace tf.range(max_length) with range(max_length), as suggested elsewhere, a similar error obtains:

OperatorNotAllowedInGraphError: Using a symbolic tf.Tensor as a Python bool is not allowed: AutoGraph did convert this function. This might indicate you are trying to use an unsupported feature.

in relation to

if predicted_id == end: break

in same class.

A reason might perhaps be found in the previous warning:

WARNING: AutoGraph could not transform <bound method ExportTranslator.call of <tensorflow.python.eager.function.TfMethodTarget object at 0x7f11a7d3ffd0>> and will run it as-is.

Any hint or workaround:

thank you very much,

Giuliano

Start by reproducing the export failure in the “Transformer model for language understanding” notebook on the reported Jupyter Notebook setup. Trace ExportTranslator.call and the Translator loop around tf.range(max_length) and predicted_id == end; done means the translator exports without the reported symbolic-tensor errors.