Python converter bugfix

[patlevin]

Motivation

The Python converter code supports writing boolean weights, but not reading them. This causes problems when reading TFJS models from Python.

Furthermore, the Python converter fails to read scalar string weights. Numeric scalar weights are read just fine, but string scalars cause an error.

Implementation

np.bool has been added to the list of supported input dtypes.

The deserialization code for string arrays has been fixed so the size calculation always returns a valid int.

Details

Scalars are stored in the weight manifest with an empty shape ([]), which is technically correct to reflect the nature of a scalar.
The string deserialization uses np.prod() to calculate the total number of items. Unfortunately, np.prod() returns 1.0 when given an empty iterable (see numpy docs under Notes).

This value cannot be used with range() later, which leads to an error in situations where a weight manifest contains string scalars (e.g. model SSD OpenImages v4).

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This change is 

[pyu10055]

Thank you for the great contribution!

Reviewable status: complete! 1 of 1 approvals obtained