[doc] Error in functional how-to example

@rhettinger

BPO	39971
Nosy	@rhettinger, @terryjreedy, @ericvsmith, @dxflores, @slateny
PRs	bpo-39971: Change examples to be runnable #32172

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assignee = None
closed_at = None
created_at = <Date 2020-03-15.16:39:23.863>
labels = ['easy', '3.11', '3.9', '3.10', 'docs']
title = '[doc] Error in functional how-to example'
updated_at = <Date 2022-03-29.07:57:47.314>
user = 'https://github.com/dxflores'

bugs.python.org fields:

activity = <Date 2022-03-29.07:57:47.314>
actor = 'eric.smith'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2020-03-15.16:39:23.863>
creator = 'dxflores'
dependencies = []
files = []
hgrepos = []
issue_num = 39971
keywords = ['patch', 'easy']
message_count = 6.0
messages = ['364247', '364275', '364346', '364708', '364709', '364710']
nosy_count = 6.0
nosy_names = ['rhettinger', 'terry.reedy', 'eric.smith', 'docs@python', 'dxflores', 'slateny']
pr_nums = ['32172']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue39971'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Hello,

A code example from the 'functional programming how-to' raises an error.

The simplest fix would be to remove the Ellipsis object from the 'line_list'.

Thank you,
Diogo

Please check below for the commands issued:

# https://docs.python.org/3/howto/functional.html#generator-expressions-and-list-comprehensions

>>> line_list = ['  line 1\n', 'line 2  \n', ...]
>>> 
>>> # Generator expression -- returns iterator
>>> stripped_iter = (line.strip() for line in line_list)
>>> 
>>> # List comprehension -- returns list
>>> stripped_list = [line.strip() for line in line_list]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
AttributeError: 'ellipsis' object has no attribute 'strip'

I don't think that was meant to be a literal example. I think that "..." here means "and other strings".

Agreed, Eric. Nevertheless, I think that this example might raise unnecessary confusion to someone new to Python, and hence the reason why I decided to open the issue. Anyhow, I trust your judgement and please feel free to leave things as is and close this issue.

PS: I really the work you did with dataclasses, and I actually explored the idea further with a small (300 LoC) library that adds runtime type checking for instances of dataclasses - if you are ever curious you can find the code on my GitHub at /dxflores/invis.

Thank you,
Diogo

In think examples should run and that '...' should be replaced by something like "' \n', ''". The blank string looks ahead to the next example, which adds ' if line != ""' to the comprehension.

Looking around further, examples meant to be executable as is are given interactive prompts and needed doctest directives

    >>> gen  #doctest: +ELLIPSIS
    <generator object generate_ints at ...>

I think that this example should get the same treatment. Non-executable examples are usually clearly non-executable because then contain undefined names line 'expr2' and 'sequence2', whereas this example starts by defining 'line_list'.

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[doc] Error in functional how-to example #84152

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[doc] Error in functional how-to example #84152

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dxflores commented on Mar 15, 2020

ericvsmith commented on Mar 16, 2020

dxflores commented on Mar 16, 2020

terryjreedy commented on Mar 20, 2020

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terryjreedy commented on Mar 20, 2020

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