parts,charm_builder: add charm-python-packages plugin property (CRAFT-552)

[cmatsuoka]

Packages listed in the charm-python-packages property are installed
before dependencies listed in the requirements file. This mirrors
python-packages that exists in the python plugin.

Signed-off-by: Claudio Matsuoka claudio.matsuoka@canonical.com

[cmatsuoka]

@heitorPB, could you check if the jinja2 installation works correctly using charm-python-packages: [markupsafe]?

[facundobatista]

100% awesome!

[heitorPB]

I wonder if the charm-python-packages entry should be in the bases instead of parts? We do support multiple OSes and we will eventually encounter a situation that we need to add a dependency to the build system for one OS but not for the other.

Same comment applies for charm.parts.build-packages.

[heitorPB]

@heitorPB, could you check if the jinja2 installation works correctly using charm-python-packages: [markupsafe]?

Is this availabe in the latest/edge snap? How do I run it locally?

[cmatsuoka]

I wonder if the charm-python-packages entry should be in the bases instead of parts? We do support multiple OSes and we will eventually encounter a situation that we need to add a dependency to the build system for one OS but not for the other.

For Python packages you can add a platform conditional such as:

$ pip install "markupsafe;sys_platform=='darwin'"
Ignoring markupsafe: markers 'sys_platform == "darwin"' don't match your environment

Same comment applies for charm.parts.build-packages.

In this case we need to add a more advanced grammar processing similar to the one used in Snapcraft.

[cmatsuoka]

Is this availabe in the latest/edge snap? How do I run it locally?

Hmm, edge snaps are built from the main branch so you can either create a snap locally (by checking out the branch and running snapcraft) or run from the checked out tree in destructive mode. Creating a local snap should be easier and safer.

[heitorPB]

Could we use this plugin to update a specific library? It appears that the problem with #551 is setuptools is not the latest version.

[cmatsuoka]

Could we use this plugin to update a specific library? It appears that the problem with #551 is setuptools is not the latest version.

Ah, that's an interesting find. Yes, setuptools should be upgraded if listed in charm-python-packages.

[cmatsuoka]

Landing it. It should be available in edge tomorrow.