[PATCH] Make pty.spawn set window size

[8vasu]

BPO	41541
Nosy	@Yhg1s, @ethanfurman, @8vasu
PRs	bpo-41541: Make pty.spawn set window size #21861
Files	pty.diff: v0.6 before.png after.png script.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 2020-08-13.17:37:00.291>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = '[PATCH] Make pty.spawn set window size'
updated_at = <Date 2020-09-15.01:08:45.199>
user = 'https://github.com/8vasu'

bugs.python.org fields:

activity = <Date 2020-09-15.01:08:45.199>
actor = 'soumendra'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-08-13.17:37:00.291>
creator = 'soumendra'
dependencies = []
files = ['49404', '49455', '49456', '49458']
hgrepos = []
issue_num = 41541
keywords = ['patch']
message_count = 15.0
messages = ['375326', '375366', '375396', '375433', '375438', '375439', '375443', '375445', '375446', '375452', '375461', '375513', '375582', '375631', '375774']
nosy_count = 3.0
nosy_names = ['twouters', 'ethan.furman', 'soumendra']
pr_nums = ['21861']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41541'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[8vasu]

The example in https://docs.python.org/3/library/pty.html that mimics script(1) can be used to reproduce the problem: since window size is not set by pty.spawn, output of "ls" becomes scattered and hard to visually parse if xterm window is not in fullscreen mode.

To fix the above issue, this patch makes pty.spawn set window size ( TIOCSWINSZ ). Also, this patch makes the code of pty.fork() more readable by defining _login_pty(); the latter is reused in spawn().

[8vasu]

OS: Linux 4.19.0-9-amd64 Debian 10 GNU/Linux

[8vasu]

Note that defining _login_pty() was not a cosmetic change; it is reused in spawn().