[Python-Dev] PEP 8 updated on whether to break before or after a binary update (original) (raw)

Guido van Rossum guido at python.org
Fri Apr 15 12:53:13 EDT 2016

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.

The head of the python-ideas discussion: https://mail.python.org/pipermail/python-ideas/2016-April/039752.html

See also the discussion in the tracker: http://bugs.python.org/issue26763

Here's the diff I applied: https://hg.python.org/peps/rev/3857909d7956

The talk by Brandon Rhodes where Knuth is referenced ([3] below): http://rhodesmill.org/brandon/slides/2012-11-pyconca/#laying-down-the-law

The key section in PEP 8 that was updated (apart from fixing up references):

Should a line break before or after a binary operator?

For decades the recommended style has been to break after binary operators. However, recent reseach unearthed recommendations by Donald Knuth to break before binary operators, in his writings about typesetting [3]_. 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)

-- --Guido van Rossum (python.org/~guido) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160415/84b8d98d/attachment.html>

More information about the Python-Dev mailing list