Bad_alloc with pyroj import in QGIS plugin

[phorgue]

Problem description

The following error may occur when trying to import pyproj into a QGIS plugin

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Abandon (core dumped)

I was able to identify that this error only occurs when the pyproj package has been installed using pip

The error does not occur if the package has been installed using a package manager, for example for ubuntu

sudo apt install python3-pyproj

This error was observed on several versions of linux (ubuntu/fedora) and on different versions of QGIS (3.28/ 3.34).
There doesn't seem to be any link with the pyproj version (installing an identical or more recent version using pip systematically causes the error)

To reproduce

Simply add :

import pyproj

to a plugin QGIS source files and install pyproj using pip. QGIS should stop while loading the plugin with the bad_alloc error.

[rouault]

I was able to identify that this error only occurs when the pyproj package has been installed using pip

fully expected and nothing one can do about, expect: never use pip with binary wheels, but in trivial use cases. And QGIS is not a trivial use case. The issue here is that pyproj installed through pip goes with its own libproj that conflicts with the libproj used by QGIS.