Docker build: opencv-python-headless fails

[bertsky]

Our last Docker release is now 9 months old. It seems there is a persistent error around the OpenCV Build:

ERROR: Failed building wheel for opencv-python-headless

Perhaps Python 3.6 is not supported anymore (no wheels on PyPI)? Or do we need more system dependencies now?

[bertsky]

@kba your CI config change still does not work on the Scrutinizer chain – it for some reason needs sudo for make deps-ubuntu. Also, on master we fail to deploy awkwardly:

/bin/sh: 1: pip: not found
The command '/bin/sh -c apt-get update && apt-get -y install software-properties-common     && apt-get update && apt-get -y install         ca-certificates         python3-dev         python3-pip         gcc         make         wget         time         curl         sudo         git     && make deps-ubuntu     && pip install --upgrade pip setuptools     && make install     && apt-get remove -y gcc     && apt-get autoremove -y     && $FIXUP     && rm -rf /build-ocrd' returned a non-zero code: 127
Makefile:217: recipe for target 'docker-cuda' failed

So make docker runs through, but docker-cuda does not.

Regarding the original error reported here – that seems to have been specific to 3.6 (and I believe it would suffice to do a simple pip install -U pip first, to get pip install cmake working; so we could even reactivate our 3.6 CI...)

[mikegerber]

I've been using this sometimes:

pip3 install -U pip
pip3 install --only-binary :all: opencv-python-headless

This installs an older opencv-python-headless, but from a wheel and without the compile time. I'd recommend always testing anything involving opencv-python-headless, we had some tricky issues with it.

[bertsky]

We did introduce a workaround in ocrd_all earlier to avoid source compilation (which effectively downgrades, but also speeds up). This warrants closing – also, 3.6 is not officially supported anymore.