os.sendfile() has improperly named parameter

[serhiy-storchaka]

BPO	38378
Nosy	@vstinner, @giampaolo, @serhiy-storchaka, @ZackerySpytz
PRs	bpo-38378: Rename parameters "out" and "in" of os.sendfile(). #16742

^{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 = <Date 2019-10-13.09:18:44.343>
created_at = <Date 2019-10-05.15:04:03.222>
labels = ['extension-modules', 'type-bug', '3.9']
title = 'os.sendfile() has improperly named parameter'
updated_at = <Date 2020-08-24.16:06:17.474>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-08-24.16:06:17.474>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-10-13.09:18:44.343>
closer = 'serhiy.storchaka'
components = ['Extension Modules']
creation = <Date 2019-10-05.15:04:03.222>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 38378
keywords = ['patch']
message_count = 6.0
messages = ['354012', '354013', '354515', '354571', '375853', '375854']
nosy_count = 4.0
nosy_names = ['vstinner', 'giampaolo.rodola', 'serhiy.storchaka', 'ZackerySpytz']
pr_nums = ['16742']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38378'
versions = ['Python 3.9']

[serhiy-storchaka]

os.sendfile() has a keyword-or-positional parameter named "in". Since it is a keyword in Python, it is not possible to pass it as a keyword argument. You can only pass it as a positional argument or using a var-keyword argument (unlikely anybody uses the latter). The preceding parameter, "out", also can not be passed by keyword because of this.

It is weird, but usually does not cause a problem. You cannot use a keyword argument, period. But it prevents os.sendfile() from converting to Argument Clinic, because Argument Clinic does not allow using Python keywords as parameter names (I already created a patch for conversion, but in needs to solve this issue first).

There are two ways to solve this issue.

1. Rename parameter "in" (and maybe "out" for consistency). "out_fd" and "in_fd" look good names (they are use in Linux manpage).

2. Make "out" and "in" positional-only parameters.

[ZackerySpytz]

See also bpo-15078.

[giampaolo]

I’m for renaming both. Since the function is about transmitting or copying (on Linux) files src_fd and dst_fd could also be good candidates.

[serhiy-storchaka]

New changeset 140a7d1 by Serhiy Storchaka in branch 'master':
bpo-38378: Rename parameters "out" and "in" of os.sendfile(). (GH-16742)
140a7d1

[vstinner]

I would prefer "2. Make "out" and "in" positional-only parameters". It would be a minor incompatible change, but it would make os.sendfile() more consistent with other functions like os.write() which only has positional-only parameters.

[vstinner]

Well, since os.sendfile(in=fd) raises a syntax error, I don't think that it's really a backward incompatible change in practice.