SSL module is missing when installing Python packages in QGIS with the new osgeo4w installer

Question

I'm trying to install a third party python package in a QGIS plugin with the following code:

import sys
import platform
import subprocess
try:
    import matplotlib
except ModuleNotFoundError:
    print('installing matplotlib')
    if platform.system() == 'Windows':
        subprocess.call([sys.exec_prefix + '/python', "-m", 'pip', 'install', 'matplotlib'])
    else:
        subprocess.call(['python3', '-m', 'pip', 'install', 'matplotlib'])

This code snipped have worked previously but with the new(?) OSGeo4W package it fails since the SSL module is not loaded? The error message looks like this:

WARNING: pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.

WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.")': /simple/matplotlib/

Is it a bug or some intended change?

Answer 1

I was able to solve this, but I did a lot of things, and am not sure what all contributed to the solution. However, I think the following step is all you need to do.

Use the osgeo4w setup (advanced install, and in administrator mode) to install the openssl module. I ran everything in the advanced installer that was on by default, but I think you could specify only the OpenSSL package.