[Guido]
After a fruitful discussion on python-ideas I've decided that it's fine to break lines *before* a binary operator. It looks better and Knuth recommends it. ... Therefore it is permissible to break before or after a binary operator, as long as the convention is consistent locally. For new code Knuth's style is suggested.
Some examples of code breaking before binary Boolean operators::
class Rectangle(Blob):
def __init__(self, width, height, color='black', emphasis=None, highlight=0): if (width == 0 and height == 0 and color == 'red' and emphasis == 'strong' or highlight > 100): raise ValueError("sorry, you lose") if (width == 0 and height == 0 and (color == 'red' or emphasis is None)): raise ValueError("I don't think so -- values are %s, %s" % (width, height)) Blob.__init__(self, width, height, color, emphasis, highlight)
Note that this code still breaks a line after a binary operator (the string formatting "%" operator in the 2nd ValueError call). But it's perfectly clear the way it is. Good taste can't be reduced to rules ;-)