I would like to use ANTLR4 with Python 2.7 and for this I did the following:

I installed the package antlr4-4.6-1 on Arch Linux with sudo pacman -S antlr4.
I wrote a MyGrammar.g4 file and successfully generated Lexer and Parser Code with antlr4 -Dlanguage=Python2 MyGrammar.g4
Now executing for example the generated Lexer code with python2 MyGrammarLexer.py results in the error ImportError: No module named antlr4. 

What could to be the problem? FYI: I have both Python2 and Python3 installed - I don't know if that might cause any trouble.
The problem was that antlr4 was only installed for Python3 and not Python2. I simply copied the antlr4 files from /usr/lib/python3.6/site-packages/ to /usr/lib/python2.7/site-packages/ and this solved the problem!
No module named antlr4