[issue20164] Undocumented KeyError from os.path.expanduser

[STINNER Victor]

STINNER Victor  added the comment:

Even if it's not exactly a duplicate of bpo-10496, the reported bug has been 
fixed. I close the issue.

--
resolution:  -> duplicate
stage: test needed -> resolved
status: pending -> closed
superseder:  -> Python startup should not require passwd entry

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[issue20164] Undocumented KeyError from os.path.expanduser

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

The behavior was changed in f2f4555d8287ad217a1dba7bbd93103ad4daf3a8 as a part 
of issue10496.

--
nosy: +serhiy.storchaka, vstinner
status: open -> pending

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[issue20164] Undocumented KeyError from os.path.expanduser

[Chris Adams]

Chris Adams added the comment:

I agree that making the code match the docs would be preferable – an unexpected 
KeyError might be easier to track down that way but it'd still surprise most 
developers.

re:pwd docs, the formatting in 
https://hg.python.org/cpython/file/8e9df3414185/Doc/library/pwd.rst makes it 
easy to miss the KeyError note – it's at the end of a paragraph after a table 
and since "entry" is a generic term it's possible to misread it as applying to 
fields within the record rather than the record itself. I think it would at 
least be worth adding a newline and perhaps explicitly noting that it applies 
to any function which returns a password database entry. 

Given that there are only two functions which it applies to, it might be best 
to simply add a note to each of them for people who use "pydoc pwd.getpwduid" 
or an IDE and don't see the module-level docs but that's getting a bit 
contrived.

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[issue20164] Undocumented KeyError from os.path.expanduser

[Terry J. Reedy]

Terry J. Reedy added the comment:

I think the doc should be considered correct and posixpath buggy.  The ntpath 
code checks for the existence of HOME and substitutes before returning the arg 
unchanged, as documented.

if 'HOME' in os.environ:
userhome = os.environ['HOME']
elif 'USERPROFILE' in os.environ:
userhome = os.environ['USERPROFILE']
elif not 'HOMEPATH' in os.environ:
return path
 
components:  -Documentation
nosy: +terry.reedy
stage: needs patch -> test needed

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[issue20164] Undocumented KeyError from os.path.expanduser

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
assignee:  -> docs@python
components: +Documentation
nosy: +docs@python
stage:  -> needs patch
versions: +Python 3.5 -Python 3.3

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[issue20164] Undocumented KeyError from os.path.expanduser

[Chris Adams]

Chris Adams added the comment:

Other than hoisting the warnings import to the top (PEP-8) that seems entirely 
reasonable to me. The user report which we got was confusing because it was 
non-obvious where it came from - a warning or other pointer would have helped 
the original reporter get an idea as to what was failing earlier.

The other two changes I'd suggest would be documentation updates:

os.path.expanduser noting that KeyError may be raised when HOME is undefined 
and pwd.getpwuid fails for the active user

pwd.getpwuid noting that KeyErrors will be raised when the underlying POSIX 
call fails

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[issue20164] Undocumented KeyError from os.path.expanduser

[Yury V. Zaytsev]

Yury V. Zaytsev added the comment:

Amusingly, it's also the case on BG/Q compute nodes. Only this morning, I 
cooked up the following patch:

--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -237,7 +237,11 @@ def expanduser(path):
 if i == 1:
 if 'HOME' not in os.environ:
 import pwd
-userhome = pwd.getpwuid(os.getuid()).pw_dir
+try:
+userhome = pwd.getpwuid(os.getuid()).pw_dir
+except KeyError:
+import warnings
+warnings.warn('Unable to auto-detect $HOME, export it or 
functionality such as user-installed modules will not work!', RuntimeWarning)
 else:
 userhome = os.environ['HOME']
 else:

I think it's a bit harsh to fail completely, but returning silently also 
doesn't sound like a good idea, so I decided to issue a warning instead; the 
wording should be probably tweaked by a native speaker of English though.

What do you think?

--
nosy: +zaytsev
type:  -> behavior
versions: +Python 3.4

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[issue20164] Undocumented KeyError from os.path.expanduser

[Chris Adams]

New submission from Chris Adams:

This is a more general version of #10496: os.path.expanduser is documented as 
returning the unmodified string if it cannot be expanded 
(http://docs.python.org/3/library/os.path.html#os.path.expanduser) but there's 
one edge case where this can fail: when running without HOME in the environment:

https://github.com/python/cpython/blob/3.3/Lib/posixpath.py#L259-L263

In this case, pwd.getpwuid is called and although it's not documented as such, 
it raises a KeyError anytime the underlying POSIX getpwuid() call fails:

https://github.com/python/cpython/blob/3.3/Modules/pwdmodule.c#L119-L120

Reproducing this deliberately:

cadams@Io:~ $ sudo -H python
Python 2.7.5 (default, Aug 25 2013, 00:04:04) 
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> import posix
>>> posix.setuid(1001)
>>> posix.seteuid(1001)
>>> os.environ.pop('HOME')
'/var/root'
>>> os.path.expanduser("~")
Traceback (most recent call last):
  File "", line 1, in 
  File 
"/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/posixpath.py",
 line 269, in expanduser
userhome = pwd.getpwuid(os.getuid()).pw_dir
KeyError: 'getpwuid(): uid not found: 1001'

Context:
* https://github.com/toastdriven/django-haystack/issues/924
* https://github.com/kennethreitz/requests/issues/1846.

--
components: Library (Lib)
messages: 207552
nosy: acdha
priority: normal
severity: normal
status: open
title: Undocumented KeyError from os.path.expanduser
versions: Python 2.7, Python 3.3

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