what is the communist party line from 1930's to 1950's?

Answer 1

It would help to know which country you're talking about.

For many years, the only communisty country was the USSR, and in that place the "party line" was whatever Stalin wanted.

In places like North Korea, China, the Eastern Block, etc it was different.

Finally, the "party line" is slang for "what did the party want you to believe." Of course, the party had all sorts of beliefs, from religion to economics to revolution to...

In other words, as a more precise question and we'll give you a better answer.