QGIS » QGIS Application

I use the OWSLib version integrated within QGIS in my plugin, to handle main OGC services (WMS/WMTS and WFS).
It's sometimes quite hard because of different lib versions. For example:

In 2.8.x
owslib version:'0.8.8'
from owslib.util import HTTPError

In 2.14.x
owslib version: '0.11.2'
from urrlib2 import HTTPError

Nothing which can't be handled by Python code. But in 2.18.4, pyrproj, an OWSLib dependency, is missing and I don't think that I can find a workaround by myself. Is it normal?

from owslib.wfs import WebFeatureService
  File "C:/PROGRA~1/QGIS2~1.18/apps/qgis/./python\\qgis\\utils.py", line 607, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:/PROGRA~1/QGIS2~1.18/apps/qgis/./python\\owslib\\wfs.py", line 18, in <module>
    from .feature import wfs100, wfs110, wfs200
  File "C:/PROGRA~1/QGIS2~1.18/apps/qgis/./python\\qgis\\utils.py", line 607, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:/PROGRA~1/QGIS2~1.18/apps/qgis/./python\\owslib\\feature\\wfs100.py", line 27, in <module>
    import pyproj
  File "C:/PROGRA~1/QGIS2~1.18/apps/qgis/./python\\qgis\\utils.py", line 607, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
ImportError: No module named pyproj