I am developing a QGIS plugin in QGIS 2.18.15 on macOS 10.13.2 and I am having some troubles with Python libraries dependencies. More specifically, my plugin will require to use an external Python library which is already installed and working in my system (both for Python 2.7 and Python 3). The problem is that apparently QGIS uses its own different version of Python (Python 2.7.10) which is not equipped with the library I need.
How can I ask QGIS to use the default system version of Python?
As an alternative, how can I add external libraries to the QGIS Python 2.7.10?