[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Guido van Rossum]

Guido van Rossum  added the comment:

PEP 8 intentionally allows users to choose whether to put the operator at the 
start or end of the line (as long as they're consistent within a file or 
project). This is to avoid a barrage of "style fixes" that are just noise.

But PEP 7 is only for CPython's own C code style, and here I don't want things 
to change. When it comes to readability of our code surely there are bigger 
fish to fry.

So I'm closing this as won't fix.

--
resolution:  -> wont fix
stage:  -> resolved
status: open -> closed

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[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
versions:  -Python 3.7

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[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

PEP 8 contains contradictory examples.

https://www.python.org/dev/peps/pep-0008/#indentation

> # No extra indentation.
> if (this_is_one_thing and
> that_is_another_thing):
> do_something()
> 
> # Add a comment, which will provide some distinction in editors
> # supporting syntax highlighting.
> if (this_is_one_thing and
> that_is_another_thing):
> # Since both conditions are true, we can frobnicate.
> do_something()
> 
> # Add some extra indentation on the conditional continuation line.
> if (this_is_one_thing
> and that_is_another_thing):
> do_something()
> 
> (Also see the discussion of whether to break before or after binary
> operators below.)

(It was already reported in other issue.)

--
nosy: +serhiy.storchaka

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[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Barry A. Warsaw]

Barry A. Warsaw  added the comment:

I personally don't think we need to change this.  C and Python are different, 
and the PEP 7 rules have been in place for ages.

+Guido

--
nosy: +gvanrossum

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[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Brett Cannon]

Change by Brett Cannon :


--
nosy: +barry

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[issue37813] PEP 7 line-breaking with binary operations contradicts Knuth's rule

[Géry]

New submission from Géry :

I have just read PEP 7 and noticed that its line-breaking recommandation in 
presence of binary operations seems to contradict its analogue in PEP 8 which 
follows Knuth's rule.

PEP 7 (https://www.python.org/dev/peps/pep-0007/#code-lay-out):

> When you break a long expression at a binary operator, the operator
> goes at the end of the previous line, and braces should be formatted
> as shown. E.g.:
> 
> if (type->tp_dictoffset != 0 && base->tp_dictoffset == 0 &&
> type->tp_dictoffset == b_size &&
> (size_t)t_size == b_size + sizeof(PyObject *))
> {
> return 0; /* "Forgive" adding a __dict__ only */
> }

PEP 8 
(https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator):

> To solve this readability problem, mathematicians and their
> publishers follow the opposite convention. Donald Knuth explains the
> traditional rule in his Computers and Typesetting series: "Although
> formulas within a paragraph always break after binary operations and
> relations, displayed formulas always break before binary operations"
> [3].
> 
> Following the tradition from mathematics usually results in more
> readable code:
> 
> # Yes: easy to match operators with operands
> income = (gross_wages
>   + taxable_interest
>   + (dividends - qualified_dividends)
>   - ira_deduction
>   - student_loan_interest)
> In Python code, 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.

--
assignee: docs@python
components: Documentation
messages: 349361
nosy: docs@python, maggyero
priority: normal
severity: normal
status: open
title: PEP 7 line-breaking with binary operations contradicts Knuth's rule
type: enhancement
versions: Python 3.7

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