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According to Knuth, it is better to break *before* a binary operator.

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gvanrossum committed Apr 15, 2016
1 parent 1a6cc45 commit c59c4376ad233a62ca4b3a6060c81368bd21e85b
Showing with 32 additions and 14 deletions.
  1. +32 −14 pep-0008.txt
@@ -151,6 +151,9 @@ Acceptable options in this situation include, but are not limited to::
that_is_another_thing):
do_something()
(Also see the discussion of whether to break before or after binary
operators below.)
The closing brace/bracket/parenthesis on multi-line constructs may
either line up under the first non-whitespace character of the last
line of list, as in::
@@ -244,20 +247,33 @@ thoughts on the indentation of such multiline ``with``-statements.)
Another such case is with ``assert`` statements.
Make sure to indent the continued line appropriately. The preferred
place to break around a binary operator is *after* the operator, not
before it. Some examples::
Make sure to indent the continued line appropriately.
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 beaking 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):
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):
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,
@@ -709,7 +725,7 @@ The following naming styles are commonly distinguished:
- ``UPPERCASE``
- ``UPPER_CASE_WITH_UNDERSCORES``
- ``CapitalizedWords`` (or CapWords, or CamelCase -- so named because
of the bumpy look of its letters [3]_). This is also sometimes known
of the bumpy look of its letters [4]_). This is also sometimes known
as StudlyCaps.
Note: When using abbreviations in CapWords, capitalize all the
@@ -1286,11 +1302,11 @@ annotations are changing.
PEP 484 recommends the use of stub files: .pyi files that are read
by the type checker in preference of the corresponding .py files.
Stub files can be distributed with a library, or separately (with
the library author's permission) through the typeshed repo [4]_.
the library author's permission) through the typeshed repo [5]_.
- For code that needs to be backwards compatible, function annotations
can be added in the form of comments. See the relevant section of
PEP 484 [5]_.
PEP 484 [6]_.
.. rubric:: Footnotes
@@ -1311,12 +1327,14 @@ References
.. [2] Barry's GNU Mailman style guide
http://barry.warsaw.us/software/STYLEGUIDE.txt
.. [3] http://www.wikipedia.com/wiki/CamelCase
.. [3] http://rhodesmill.org/brandon/slides/2012-11-pyconca/#laying-down-the-law
.. [4] http://www.wikipedia.com/wiki/CamelCase
.. [4] Typeshed repo
.. [5] Typeshed repo
https://github.com/python/typeshed
.. [5] Suggested syntax for Python 2.7 and straddling code
.. [6] Suggested syntax for Python 2.7 and straddling code
https://www.python.org/dev/peps/pep-0484/#suggested-syntax-for-python-2-7-and-straddling-code

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