Development of a plugin which depends on an external Python library

Question

I'm developing a Python plugin, the target is integrating into QGIS the functionalities of a PyPI Python library called 'elevation'.

Is there an OS independent way of installing external Python libraries and making them available to the Python plugins?

I already know the different system specific procedures for installing an external Python dependency, what I'd like to do is to distribute my plugin across different environments without making people go crazy.

What I already know

Searching the web and other similar questions it seems that there isn't an OS independent solution.

Windows users

Python is packaged and distributed inside the QGIS package, so in order to install external Python libraries you have to go through the OSGeo4W Shell and use pip from there.

related links:

• QGIS standalone and Python modules
• Installing Python setuptools into OSGeo4W Python
• How to install 3rd party python libraries for QGIS on Windows?

OS X Users

In this case QGIS uses the built-in Python which is prepackaged inside OS X and located at:

/usr/bin/python

The issue here is that the default installed pip has some limitations and requires too many privileges.

A quick workaround is to use home-brew to install Python so that your pip can run against a user-modifiable Python framework. See the details of this approach here.

After installing all the Python libraries via pip, you just need to add their directories to the PATH variable.

Alternative way for OS X users

Inside the plugin Python code you can use the pip provided by the system in order to install the required packages. Then you can make the just installed package reachable adding it to the path.

import sys
import pip
pip.main(['install','--target=/Devel/test', 'elevation'])
sys.path.append("/Devel/test")

Homemade but working solution (tested on both Linux and OS X)

I decided to go for the alternative way since it allows to keep the library update and maintenance separated from the plugin. Every time a new user installs the plugin the latest version of the elevation library is directly downloaded and installed by pip inside a subdirectory of the plugin.

self.plugin_dir = os.path.dirname(__file__)
self.elevation_dir = os.path.join(self.plugin_dir, 'elevation')

# Checking the presence of elevation library
try:
    import elevation
except:
    pip.main(['install', '--target=%s' % self.elevation_dir, 'elevation'])
    if self.elevation_dir not in sys.path:
        sys.path.append(self.elevation_dir)

Answer 1

The most convenient solution for users of the plugin is to bundle wheel inside your plugin. Download wheel, place it in your plugin folder and import it from there.

try:
    import elevation
except ImportError:
    import sys
    import os
    this_dir = os.path.dirname(os.path.realpath(__file__))
    path = os.path.join(this_dir, 'elevation-x.y.z-py2.py3-none-any.whl')
    sys.path.append(path)
    import elevation

Answer 2

I worked on this a little bit on a project recently. Unfortunately there's really not a great way to achieve this. Your solution is very similar to what I came up with, but there's no guarantee the user even has pip installed.

I ended up including a copy of get_pip.py and using execfile() to run it in the case when it's not available.

Similar to your final solution:

self.plugin_dir = os.path.dirname(__file__)

try:
    import pip
except:
    execfile(os.path.join(self.plugin_dir, get_pip.py))
    import pip
    # just in case the included version is old
    pip.main(['install','--upgrade','pip'])

try:
    import somelibrary
except:
    pip.main(['install', 'somelibrary'])

An alternative, of course, would be to include the library itself in your plugin's directory. You risk providing an old version, but theoretically it won't matter.

Answer 3

This worked for me (in def run(self)):

    def load_libraries(self):
        import_path = os.path.join(self.plugin_dir, 'lib/python2.7/site-packages')
        sys.path.insert(0, import_path)

and setting up a virtualenv.

With Windows it seems to be a different story though. I had trouble installing matplotlib.

Answer 4

I suffered through this issue to run Python scripts in QGIS which depends on an external Python library. The most straightforward solution is to install Boundless Desktop that comes with the command line and installs its own python. Using the command line you can run and install (using pip) any external package of python.

Answer 5

Perhaps you can try virtualenv to install external dependencies. This way, you don't have to worry (as much) about the system environment.

https://www.fullstackpython.com/application-dependencies.html

Answer 6

As QGIS is using the pre-installed python on a Linux system you can either do sudo pip install <package>, but that clutters the default setup.

Better is to create a virtual environment (for example /home/<user>/QGIS/venv), activate the virtual environment and then install your <package> as usual. What you have to do next is inside the script add the following lines before import the <package>:

import_path = os.path.join('/home/<user>/QGIS/venv/lib/python3.7/site-packages')
sys.path.insert(0, import_path)
import <package>

Your installed <package> will now be found.