Question

Is there a reason why this doesn’t work in Python?

if 1 != 1 or
   2 != 2:
   print 'Something is wrong...'

Answer 1

Perhaps this prevents a grammar ambiguity, but I feel that this behaviour is in the spirit of PEP 20, specifically ‘Simple is better than complex’ (among others). In other words, ‘Unless you have a good reason, why should expressions span multiple lines?’. If you have a good reason, the syntax devices to get around this are provided.

[edit]
I did some more reading, and there are a few references of interest:

• The lexical definition of statements says that logical lines end in with a newline. Each case for adding an implicit continuation becomes and exceptional case.
• PEP 3125 for Python 3, proposed removing slash (\) continuation, but was rejected due to lack of support.
  • Discussion in the mailing list reminds us that parenthetical continuation occurs because newlines do not end statements while parenthesis remain unbalanced.
  • In that same thread, Guido opposes the change because errors like the following are disguised:

---

    x = y+    # Used to be y+1, the 1 got dropped
    f(x)

My final point is, the slash acts (or open parens) acts as a reminder that the statement is continued on the next line. Depending on your indentation, it’s possible that the continuation could be mistaken for a separate statement (which I think this other response touches on).