HTTPServer server.py assumes sys.stderr != None

[grismar]

BPO	28294
Nosy	@gvanrossum, @orsenthil, @bitdancer, @Mariatta, @Grismar
Files	issue28294.patch

^{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 2016-10-02.00:10:14.401>
created_at = <Date 2016-09-28.07:08:24.924>
labels = ['easy', 'type-bug', 'library']
title = 'HTTPServer server.py assumes sys.stderr != None'
updated_at = <Date 2016-10-02.12:19:57.853>
user = 'https://github.com/grismar'

bugs.python.org fields:

activity = <Date 2016-10-02.12:19:57.853>
actor = 'grismar'
assignee = 'none'
closed = True
closed_date = <Date 2016-10-02.00:10:14.401>
closer = 'r.david.murray'
components = ['Library (Lib)']
creation = <Date 2016-09-28.07:08:24.924>
creator = 'grismar'
dependencies = []
files = ['44890']
hgrepos = []
issue_num = 28294
keywords = ['patch', 'easy', 'needs review']
message_count = 11.0
messages = ['277593', '277617', '277686', '277705', '277739', '277782', '277813', '277822', '277823', '277834', '277888']
nosy_count = 5.0
nosy_names = ['gvanrossum', 'orsenthil', 'r.david.murray', 'Mariatta', 'grismar']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue28294'
versions = ['Python 3.5']

[grismar]

On line 556 of server.py, the sys.stderr.write assumes that sys.stderr is assigned and not None.

However, when developing Windows services using the pypiwin32 library (as an example), sys.stderr == None

A workaround is to override the log_message method of the BaseHTTPRequestHandler, but it seems to me that the method should not assume the availability of stderr?

[bitdancer]

That would be masking an error, I think. What might be reasonable would be to convert it to use the logging module in 3.7.

[orsenthil]

Using logging, instead of sys.stderr would be a welcome change in this module.

[Mariatta]

I'm interested to work on a patch for this, if no one started yet.

[Mariatta]

use the logging module instead of sys.stderr

[gvanrossum]

I wonder if we shouldn't close this as "won't fix" and tell the OP to override the log_message() method. It's kind of curious to complain about *this* dependency on sys.stderr existing and working, since there are probably 1000s of other places in the stdlib that also depend on that.

[bitdancer]

That would be my answer if we aren't switching to logging. I would consider that an enhancement, but are there reasons to not do that?

[grismar]

Closing and not fixing is fair enough - I did not realize that this would be an issue that occurs in many places in stdlib.

I realize this is not a help forum, so I will ask elsewhere to see if there's some way to redirect all of sys.stderr in scenarios like these (running a service), because tracking down an issue like this takes a lot of time and finding the issue buried in a standard library caught me off guard.

[gvanrossum]

A problem with switching to logging is the API design.

There are three functions, log_request(), log_error() and
log_message(). The former two call the latter. The API explicitly
encourages overriding log_message() to customize logging. But it has
no way to know whether it's called from log_error(), log_request(), or
directly.

So how is it to choose logging levels? I imagine log_request() should
log at the INFO level, log_error() at the ERROR level, and let's say
that direct calls to log_message() should also log at the INFO level
(from looking at the few calls). So how should log_error() distinguish
itself to log_message() without breaking apps that override the
latter?

[bitdancer]

OK, lets close this won't fix, then. Especially since aiohttp does use logging already....

Sorry, Mariatta. Thanks for the patch, but we aren't going to use it.

[grismar]

Breaking the API isn't good, but it will only break if log_message doesn't *receive* all messages, because that's what people who override it count on.

If there's some way of detecting who called log_message, you could use the appropriate log level on logging without compromising the API. But the only way I see without changing the signature of log_message is through inspect functions like getouterframes and that seems way nastier than these functions merit...