Don't use \
, use parenthesis:
if (CONDITION1 or
CONDITION2 or
CONDITION3):
and you can add comments at will:
if (CONDITION1 or # condition1 is really cool
CONDITION2 or # be careful of conditon2!
CONDITION3): # see document A sec. B for info
Python allows for newlines in a parenthesised expression, and when using comments that newline is seen as being located just before the comment start, as far as the expression is concerned.
Demo:
>>> CONDITION1 = CONDITION2 = CONDITION3 = True
>>> if (CONDITION1 or # condition1 is really cool
... CONDITION2 or # be careful of conditon2!
... CONDITION3): # see document A sec. B for info
... print('Yeah!')
...
Yeah!