[New-bugs-announce] [issue21545] Tutorial: examples and comment about mutation methods

[Terry J. Reedy]

New submission from Terry J. Reedy:

The Tutorial section More on Lists
https://docs.python.org/3.4/tutorial/datastructures.html#more-on-lists includes list.pop but ignores it in the example and final comment. I think the examples should be augmented and the comment modified.

1. (simplest) End the example block with

>>> a.pop()
1234.5
>>> a
[-1, 1, 66.25, 333, 333]

2. The comment says "You might have noticed that methods like insert, remove or sort that modify the list have no return value printed – they return None. [1] This is a design principle for all mutable data structures in Python." [The footnote says "[1] Other languages may return the mutated object, which allows method chaining, such as d->insert("a")->remove("b")->sort();."]

Inserting 'only' before 'modify' makes the statement true even now with .pop added. I think 'the default' should be added before 'None', but that would be optional. I do not think .pop needs to be explicitly mentioned here since the point of the comment is to explain the lack of a printed return value, and .pop does have a printed return value.

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assignee: docs at python
components: Documentation
messages: 218857
nosy: docs at python, ncoghlan, terry.reedy
priority: normal
severity: normal
stage: needs patch
status: open
title: Tutorial: examples and comment about mutation methods
type: behavior
versions: Python 2.7, Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21545>
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