Idiomatic Python says:
Use backslashes as a last resort
So, if using parentheses () is possible, avoid backslashes.
If you have a a.train.wreck.that.spans.across.a.dozen.cars.and-multiple.lines.across.the.whole.trainyard.and.several.states() do something like:
lines = a.train.wreck.that.spans.across.a.dozen.cars.and-multiple.lines
lines.across.the.whole.trainyard.and.several.states()
Or, preferably, refactor your code. Please.