https://github.com/kislyuk/argcomplete allows for easy integration with bash auto-completion.

In the file defining the Alkene functional group (stk.molecular.functional_groups.alkene.py), lines 103 and 116 return self.atom1 and self.atom2.
atom1 and atom2 do not exist.
Should be return self._atom1 and return self._atom2.

This issue is not picked up with the current tests so suggests a need to see if each atom can be retrieved successfully ( get_carbon1 etc.) for each fu