Avoid calling isatty() for most open() calls

[collinanderson]

BPO	45944
Nosy	@pitrou, @benjaminp, @serhiy-storchaka, @eryksun, @collinanderson
PRs	bpo-45944: Avoid calling isatty() for most open() calls #29870

^{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 2021-12-01.05:08:15.763>
labels = ['3.11', 'expert-IO', 'performance']
title = 'Avoid calling isatty() for most open() calls'
updated_at = <Date 2021-12-01.11:53:13.388>
user = 'https://github.com/collinanderson'

bugs.python.org fields:

activity = <Date 2021-12-01.11:53:13.388>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['IO']
creation = <Date 2021-12-01.05:08:15.763>
creator = 'collinanderson'
dependencies = []
files = []
hgrepos = []
issue_num = 45944
keywords = ['patch']
message_count = 3.0
messages = ['407427', '407434', '407444']
nosy_count = 6.0
nosy_names = ['pitrou', 'benjamin.peterson', 'stutzbach', 'serhiy.storchaka', 'eryksun', 'collinanderson']
pr_nums = ['29870']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue45944'
versions = ['Python 3.11']

Linked PRs

• gh-90102: Optimize io.FileIO.isatty() #112495
• gh-90102: Remove isatty call during regular open #124922
• gh-90102: Fix pyio return value #125089

[collinanderson]

isatty() is a system call on linux. Most open()s are files, and we're already getting the size of the file. If it has a size, then we know it's not a atty, and can avoid calling it.