Adding missing python packages to QGIS Plugin?

Question

In our plugin, we dependent on some external python packages. Some are available in QGIS, some (like pandas or fiona) are not.

I've written small script, which checks requirements and if something is missing, it is automatically installed.

install_deps.py:

import pathlib
import sys

plugin_dir = pathlib.Path(__file__).parent.parent


try:
    import pip
except ImportError:
    exec(
        open(str(pathlib.Path(plugin_dir, 'scripts', 'get_pip.py'))).read()
    )
    import pip
    # just in case the included version is old
    pip.main(['install', '--upgrade', 'pip'])

sys.path.append(plugin_dir)

with open(str(plugin_dir / 'requirements.txt'), "r") as requirements:
    for dep in requirements.readlines():
        dep = dep.strip().split("==")[0]
        try:
            __import__(dep)
        except ImportError as e:
            print("{} not available, installing".format(dep))
            pip.main(['install', dep])

In the main file of python plugin, I just have import install_deps and missing modules are pip-installed automatically.

Disadvantage is, that this short "check" is done every time QGIS is starting (with the plugin activate).

Not sure, if there is better approach, than this?

Answer 1

Don't do this.

It would be super irritating if some QGIS plugin would install/upgrade python packages behind the user's back. Please don't do this unless you isolate this 100% to just your own plugin, which is either impossible or incredibly complex.

You risk breaking other plugins, breaking other software, breaking the user's system!

Imagine if another plugin always installed its own specific pandas version that is incompatible with yours.

Instead:

• make a prominent note about which packages in which versions are needed
• make your plugin try and fail gracefully
• let the user themselves handle external dependencies

Answer 2

Like bugmenot123 said, don't do this behind the user's back.

Let the code check wether a file is present or not? When it is present the code has never been run. When it has finished running the first time it will delete the (rename) the install_deps.py file.

import os

if os.path.isfile('install_deps.py'):
    print('WARNING: new dependies will be installed....')
    import install_deps
    install_deps.installer_func
    os.rename('install_deps.py', 'install_deps.installed')
else:
    pass

Place youre code into a function:

import pathlib
import sys

def installer_func:
    # youre code from install_deps.py

Answer 3

The place were the blessed route to a solution will be, if it can be found, is PIP dependencies for Python plugins QGIS enhancement proposal. It's a hard problem to solve. That thread contains exploration of what doesn't work well enough and some interim approaches.

The cleanest to my eye is https://github.com/qgis/QGIS-Enhancement-Proposals/issues/202#issuecomment-815844271, an eye that has read throught things but not tried to implement anything! So do read and think through the rest.

...we solved the problem of conflicting versions of libraries with our plugins when I was working for Boundles was to alter the path through sites and ship all the dependencies within the plugin itself.

I can't remember the details @volaya knows probably more. Here is an example of a plugin that was doing that: https://github.com/planetfederal/qgis-geoserver-plugin/blob/master/geoserverexplorer/extlibs/site.py

So, each plugin imported its dependencies from a module plugin_namespace.extlibs actually insulating them from other plugins. IIRC it was working well but I can't remember if it led to issues with binaries.