fix cyclegan save error

[k2ok3i]

This is the solution for # 691
This fixes an issue that caused an error at CycleGan's Model Checkpoint.

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[fchollet]

Thanks for the PR!

[fchollet]

Why this line?

[fchollet]

Can we remove this line? What happens if we do?

[k2ok3i]

Without this line we get this error.
I followed the error message and tried to specify the input shape using the build method and got the same error.

ValueError Traceback (most recent call last)
in ()
42 tf.data.Dataset.zip((train_horses, train_zebras)),
43 epochs=1,
---> 44 callbacks=[plotter, model_checkpoint_callback],
45 )

1 frames

/usr/local/lib/python3.7/dist-packages/keras/utils/traceback_utils.py in error_handler(*args, **kwargs)
65 except Exception as e: # pylint: disable=broad-except
66 filtered_tb = _process_traceback_frames(e.traceback)
---> 67 raise e.with_traceback(filtered_tb) from None
68 finally:
69 del filtered_tb

/usr/local/lib/python3.7/dist-packages/keras/saving/saving_utils.py in raise_model_input_error(model)
92 # If the model is not a Sequential, it is intended to be a subclassed model.
93 raise ValueError(
---> 94 f'Model {model} cannot be saved either because the input shape is not '
95 'available or because the forward pass of the model is not defined.'
96 'To define a forward pass, please override Model.call(). To specify '

ValueError: Model <main.CycleGan object at 0x7f3e527afb10> cannot be saved either because the input shape is not available or because the forward pass of the model is not defined.To define a forward pass, please override Model.call(). To specify an input shape, either call build(input_shape) directly, or call the model on actual data using Model(), Model.fit(), or Model.predict(). If you have a custom training step, please make sure to invoke the forward pass in train step through Model.__call__, i.e. model(inputs), as opposed to model.call().

The only way to fix it was to add this line.

[fchollet]

What version of TF are you using?

You don't need to add this line then. Those who want to save the model can add the line (but this example doesn't save the model and thus doesn't need it) -- and the error message tells them exactly what they need to do.

[k2ok3i]

The versions used were 2.8.2 and 2.9.2.
I have removed this line.

[fchollet]

Please run black on the file to fix the code style.

[k2ok3i]

In this problem, the error occurred because the input shape was not given.
Therefore, the input shape was given using the compute_output_shape method.

The code style has been corrected.

[fchollet]

LGTM, thanks!

[emily-stueckelmaier]

Hi all,
I was trying to run the code without cycle_gan_model.compute_output_shape(input_shape=(None, 256, 256, 3))
Without it I get the same saving error, even if i run it in the latest colab version. But with the line cycle_gan_model.compute_output_shape(input_shape=(None, 256, 256, 3)) the error is fixed

So please add this line to the code for other users :)