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

[Géry]

New submission from Géry <gery.ogam at gmail.com>:

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 at python
components: Documentation
messages: 349361
nosy: docs at 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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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37813>
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