Support Python 3.9

[mikegerber]

In a Python 3.9 venv:

% python --version                                                                                      master 
Python 3.9.5
% pip install -e .                                                                                          master 
Obtaining file:///home/mike/devel/ocrd_calamari
Collecting h5py<3
  Using cached h5py-2.10.0.tar.gz (301 kB)
ERROR: Could not find a version that satisfies the requirement tensorflow<2.5.0,>=2.3.0rc2 (from ocrd-calamari) (from versions: 2.5.0rc0, 2.5.0rc1, 2.5.0rc2, 2.5.0rc3, 2.5.0, 2.6.0rc0)
ERROR: No matching distribution found for tensorflow<2.5.0,>=2.3.0rc2

Related to #64 and possibly #61.

[bertsky]

Related to #64

Yes, the TF<2.5 req is from #64, but that in turn was only necessary to protect the older h5py<3 from becoming dysfunctional when TF 2.5 was released.

At the time, I did not know that Calamari 1.0 models were in fact compatible with h5py 3 on TF 2.5 – I just assumed your restriction must have been the result of a diagnosis to the contrary (and I did see similar incompatibilities elsewhere).

But 15bcfde's changelog hints that this was just transient: TF 2.4 itself at the time was not compatible with h5py 3.

So, unless I am missing something, the solution to this – as well as to ocrd_all conflicts – is to just ditch both the maximum h5py and TF restrictions.

[mikegerber]

Yes, the TF<2.5 req is from #64, but that in turn was only necessary to protect the older h5py<3 from becoming dysfunctional
But 15bcfde's changelog hints that this was just transient: TF 2.4 itself at the time was not compatible with h5py 3.

That was the usual dance around shortcomings of pip, i.e. install compatible versions of TF and h5py. I'll commit a fix that seems to work for Python 3.6 and Python 3.9!

[mikegerber]

This comes up again with #61 - Calamari 2.1 depends on TF 2.4.x, which is not PyPI-available for Python >= 3.9... Great joy!

[mikegerber]

Calamari-OCR/calamari#304

[mikegerber]

This is not an issue at the moment, but might come up again with Calamari 2.