For comprehensive listing of what's going on in Paris while you are there, buy one of the weekly guides, Pariscope (with an English-language supplement) or L'Officiel des Spectacles.
Knowing what is going on in Paris is impossible because of the lack of guides. 
mnli hypothesis: Knowing what is going on in Paris is impossible because of the lack of guides.  premise: For comprehensive listing of what's going on in Paris while you are there, buy one of the weekly guides, Pariscope (with an English-language supplement) or L'Officiel des Spectacles.