gh-143420: Clarify sequence behavior for slice indexes #143422
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This explain what happens when for negative start or stop arguments of big magnitude. Also reference sequence term in the :mod:`array` docs.
skirpichev
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needs backport to 3.13
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CC @hugovk, per experts index (see issue thread on proposal to remove redundant methods from array docs) |
picnixz
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Jan 10, 2026
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| This module defines an object type which can compactly represent an array of | ||
| basic values: characters, integers, floating-point numbers. Arrays are sequence | ||
| basic values: characters, integers, floating-point numbers. Arrays are :term:`sequence` |
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Maybe directly say "mutable sequence" types?
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| ``len(s)``. If *i* or *j* is less than ``-len(s)``, use ``0``. | ||
| If *i* is omitted or ``None``, use ``0``. If *j* is omitted or | ||
| ``None``, use ``len(s)``. If *i* is greater than or equal to *j*, the slice is |
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We could compress this as:
If *i* or *j* is greater than ``len(s)`` (respectively, ``-len(s)``), use ``len(s)`` (respectively, ``0``). If *i* (respectively, *j*) is
omitted or ``None``, use ``0`` (respectively ``len(s)``).However, for readers not familiar with the If X (resp. X'), then Y (resp. Y') construction, it may be very confusing. An alternative would be to have a bullet point list though it could make the paragraph vertically large. And fina alternative is to group those sentences:
The slice of *s* from *i* to *j* is defined as the sequence of items with index *k* such that ``i <= k < j``.
If *i* or *j* is greater than ``len(s)``, use ``len(s)``.
If *i* or *j* is less than ``-len(s)``, use ``0``.
If *i* is omitted or ``None``, use ``0``.
If *j* is omitted or ``None``, use ``len(s)``.
If *i* is greater than or equal to *j*, the slice is empty.
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Yes, that "respectively" is confusing. And let's not compress further, dense text is harder to read and understand.
I like that final one, with bullets, and slightly re-ordered with simpler cases first:
The slice of *s* from *i* to *j* is defined as the sequence of items with index *k* such that ``i <= k < j``.
* If *i* is omitted or ``None``, use ``0``.
* If *j* is omitted or ``None``, use ``len(s)``.
* If *i* or *j* is less than ``-len(s)``, use ``0``.
* If *i* or *j* is greater than ``len(s)``, use ``len(s)``.
* If *i* is greater than or equal to *j*, the slice is empty.
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This explain what happens when for negative start or stop arguments of big magnitude.
Also reference sequence term in the :mod:
arraydocs.sequence.insert#143420📚 Documentation preview 📚: https://cpython-previews--143422.org.readthedocs.build/en/143422/library/stdtypes.html