Guys, I have some trouble finding the extensions directory in Plone5 to add my external method . I need to place a python script in that directory.
Using External Methods (a Zope thing) is still possible but neither supported nor used nowadays. If you need to add Python functionality to Plone site then wrap it into a browser view.
You can yourself add an Extensions folder in any plone product. Then include an init.py in the Extensions folder. We use it - although is kind of legacy - for migration of data.
Oh what a hack, but what a LOVELY hack The file you have to include is
__init__.py, though I'm not sure if it needs to contain anything.