textwrap.wrap: add control for fonts with different character widths

[parent5446]

BPO	12499
Nosy	@birkenfeld, @amauryfa, @merwok, @serhiy-storchaka, @xi
PRs	gh-56708: support custom len function in textwrap.wrap #28136
Files	textwrap.py-widthfunction-2011-07-04_22-57-49_r71219+.diff: Addition of custom width function to textwrap.py.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2011-07-05.03:03:24.379>
labels = ['type-feature', 'library', '3.11']
title = 'textwrap.wrap: add control for fonts with different character widths'
updated_at = <Date 2021-09-03.18:32:07.776>
user = 'https://bugs.python.org/parent5446'

bugs.python.org fields:

activity = <Date 2021-09-03.18:32:07.776>
actor = 'eric.araujo'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2011-07-05.03:03:24.379>
creator = 'parent5446'
dependencies = []
files = ['22574']
hgrepos = []
issue_num = 12499
keywords = ['patch', 'needs review']
message_count = 6.0
messages = ['139828', '139829', '139881', '139894', '231092', '401011']
nosy_count = 6.0
nosy_names = ['georg.brandl', 'amaury.forgeotdarc', 'eric.araujo', 'parent5446', 'serhiy.storchaka', 'xi2']
pr_nums = ['28136']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue12499'
versions = ['Python 3.11']

[parent5446]

Originally from http://bugs.python.org/issue12485 but separated.

The textwrap modules uses len to determine the length of text, but in many (if not most) fonts, the width of a character differs depending on the letter, so it would be useful to have an option to pass a custom function that returns the width of a given string of text.

[amauryfa]

About the patch: the function should not be passed to the constructor, it could be a regular method that can be overridden in subclasses.

[merwok]

Amaury, do you think it’s more common to subclass TextWrapper than just instantiate it? I find the proposed API (an argument to __init__) very intuitive.

[parent5446]

Normally I would have just added it as a function to be overloaded, but because of the nature of the textwrap.wrap function (all kwargs are passed to the TextWrapper constructor) I thought it made a lot more sense to keep it as an argument to __init__.

[serhiy-storchaka]

Both approaches can be combined. It could be a regular overridable method, and it could be overridded for an instance if corresponding argument is specified. See the default method and parameter of JSON encoder.

I slightly hesitate about the name. Is "width_func" the best of names?

[merwok]

A PR was opened for this. text_len is used as param/attribute name.