[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

Per discussion, expanduser('~other') is considered unreliable, and we shouldn't 
add new functions that call through to it. Resolving as 'rejected'.

--
resolution:  -> rejected
stage: patch review -> resolved
status: open -> closed

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

So far I've been keen to keep the Path and AbstractPath APIs the same, but 
perhaps this case warrants an exception.

What if AbstractPath lacked both home() and expanduser(), and those methods 
only existed on Path? Of all the methods on Path, these two are the *least* 
useful for non-local filesystems.

We can then circle back round to this issue when the fate of expanduser() 
becomes clearer.

Does that sound any good?

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

Totally valid!

I suppose it hinges on the relatively likelihood/unlikelihood of us being able 
to make `expanduser('~foo')` reliable in future. On this question I'm relieved 
to defer to the experts!

@eryksun: penny for your thoughts?

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Steve Dower]

Steve Dower  added the comment:

Yeah, that's all reasonable.

But why wouldn't we go the other way and say "getting a user directory for a 
different user is not supported and all existing ways to do it are now 
deprecated"?

I know you think that's not a relevant argument right now, but it is a related 
one, and any change to the status quo justifies bringing it back up. So now 
it's up, we want to decide on it before we make another change that could run 
counter to the overall direction.

So I think, given the unlikelihood of us being able to properly fix the 
functionality, that we should deprecate getting another user's directory 
completely and, hence, not add new entry points to deprecated API.

Convince me I'm wrong :)

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

In the previous comment, I was referring to bpo-39899 when I referred to "my 
patch". Long day! :D

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

Thanks very much for taking a look. I can understand the view that, given the 
unreliability of `os.path.expanduser('~foo')`, we shouldn't be making that 
functionality *more* available.

My argument for this being a reasonable change is as follows:

Firstly, `os.getcwd()` is a more fundamental operation than 
`os.path.absolute()`. In both pathlib and os.path, the `absolute()` 
implementation is built on the `getcwd()` implementation. The process is: call 
the more fundamental operation, and append whatever else was passed as an 
argument.

Analagously, `gethomedir()` is a more fundamental operation than 
`expanduser()`. In the same way, `expanduser()` can call a more fundamental 
operation and then append the path passed in.

Secondly, for a `pathlib.AbstractPath` implementation, it's a much cleaner API 
to have `getcwd()` and `gethomedir()` as abstract methods with identical 
signatures, and `absolute()` and `expanduser()` with default implementations.

Thirdly, if there's are issues with the implementation for retrieving other 
user's home directories, those should be treated as individual issues with 
their own bugs, and we should add suitable warnings in the docs in the short 
term. My patch should make these cases *easier* to solve as we no longer have 
two competing implementations of the same thing.

Finally, I don't think anyone is going to see `home('barney')` in the docs and 
decided to retrieve a user's home directory on a whim. If someone *does* need 
to retrieve another user's home directory, they're going to use `Path('~' + 
user).expanduser()` if `Path.home(user)` isn't available.

My argument mostly comes from the similarities I perceive between 
getcwd/absolute and gethomedir/expanduser. We don't expect users to 
`os.path.absolute('.')` to get the current working directory, after all! But 
perhaps I've overestimated the similarities here. Any thoughts?

Thanks again for taking a look.

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Steve Dower]

Steve Dower  added the comment:

I'm not convinced this is a good change, mainly for the reasons Serhiy 
mentioned (and others have mentioned when I've spoken with them privately).

What would you do with your custom subclass if home() did not have this 
argument?

--
nosy: +steve.dower

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Eryk Sun]

Eryk Sun  added the comment:

> 3. Worth fixing in `ntpath.expanduser()` 

To expand on the suggestion in msg390507, here's a demo that implements getting 
the profile path of a local user account, with support for the special profile 
directories "Default", "Public", and "ProgramData" (i.e. ALLUSERSPROFILE).

ERROR_NONE_MAPPED = 1332

def get_profile_path(name):
if not isinstance(name, str):
raise TypeError(f'name must be str, not {type(name).__name__}')
profile_list = r'Software\Microsoft\Windows 
NT\CurrentVersion\ProfileList'
if name.lower() in ('default', 'public', 'programdata'):
subkey = profile_list
value = name
else:
try:
sid = lookup_account_name(name)[0]
except OSError as e:
if e.winerror != ERROR_NONE_MAPPED:
raise
raise KeyError(f'name not found: {name}')
subkey = f'{profile_list}\\{sid}'
value = 'ProfileImagePath'
try:
with winreg.OpenKey(winreg.HKEY_LOCAL_MACHINE, subkey) as hkey:
path, dtype = winreg.QueryValueEx(hkey, value)
except FileNotFoundError:
raise KeyError(f'name not found: {name}')
if dtype == winreg.REG_SZ:
return path
if dtype == winreg.REG_EXPAND_SZ:
return winreg.ExpandEnvironmentStrings(path)
raise TypeError('profile path value must be a string type (1 or 2), '
 f'not {dtype}')

For example:

>>> print(get_profile_path('administrator'))
C:\Users\Administrator

>>> print(get_profile_path('default'))
C:\Users\Default

>>> print(get_profile_path('public'))
C:\Users\Public

>>> print(get_profile_path('programdata'))
C:\ProgramData

>>> print(get_profile_path('system'))
C:\Windows\system32\config\systemprofile

>>> print(get_profile_path('localservice'))
C:\Windows\ServiceProfiles\LocalService

>>> print(get_profile_path('networkservice'))
C:\Windows\ServiceProfiles\NetworkService

For lookup_account_name(), _winapi.LookupAccountName(system_name, account_name) 
has to be implemented. It should convert the SID result to string form via 
ConvertSidToStringSidW() and return the tuple (sid_string, domain_name, 
account_type). Here's a ctypes prototype implementation of 
lookup_account_name():

import ctypes

lsalookup = ctypes.WinDLL(
'api-ms-win-security-lsalookup-l2-1-0', use_last_error=True)
sddl = ctypes.WinDLL('api-ms-win-security-sddl-l1-1-0', use_last_error=True)
heap = ctypes.WinDLL('api-ms-win-core-heap-l2-1-0', use_last_error=True)

ERROR_INSUFFICIENT_BUFFER = 122

def lookup_account_name(name):
sid = (ctypes.c_char * 1)()
cb = ctypes.c_ulong()
cch = ctypes.c_ulong()
name_use = ctypes.c_ulong()
lsalookup.LookupAccountNameW(None, name, sid, ctypes.byref(cb),
None, ctypes.byref(cch), ctypes.byref(name_use))
error = ctypes.get_last_error()
if error != ERROR_INSUFFICIENT_BUFFER:
raise ctypes.WinError(error)

sid = (ctypes.c_char * cb.value)()
domain_name = (ctypes.c_wchar * cch.value)()
success = lsalookup.LookupAccountNameW(None, name, sid,
ctypes.byref(cb), domain_name, ctypes.byref(cch),
ctypes.byref(name_use))
if not success:
raise ctypes.WinError(ctypes.get_last_error())

ssid = ctypes.c_wchar_p()
if not sddl.ConvertSidToStringSidW(sid, ctypes.byref(ssid)):
raise ctypes.WinError(ctypes.get_last_error())
string_sid = ssid.value
heap.LocalFree(ssid)

return string_sid, domain_name.value, name_use.value

--
nosy: +eryksun

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

Thanks for the feedback.

1. We can check the return value, like we do in `Path.expanduser()`
2. Seems like expected behaviour?
3. Worth fixing in `ntpath.expanduser()` I think. See Eryk Sun's comment here: 
https://bugs.python.org/issue39899#msg390507

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

os.path.expanduser() has flaws.

1. It can return an argument unchanged if failed to determine the home 
directory.
2. On Unix it does not work for users not found in the local password database.
3. On Windows it only guess the home directory for other users. It does not 
work if you have home directory at nonstandard location (i.e. on other disk).

Until we fix these flaws it is better to not add flawed by design feature in 
pathlib.

--
nosy: +serhiy.storchaka

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Change by Barney Gale :


--
keywords: +patch
pull_requests: +24004
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/25271

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

Barney Gale  added the comment:

I should add that this is part of a plan to spin out some `Path` methods into a 
new `UserPath` class. Notably, in this case, `UserPath.expanduser()` will call 
`self.home()` under-the-hood. This is done to reduce the surface area of 
abstract methods that subclasses of `UserPath` need implement. More discussion 
here: https://discuss.python.org/t/make-pathlib-extensible/3428

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[issue42998] pathlib.Path: add `username` argument to `home()`

[Barney Gale]

New submission from Barney Gale :

The `pathlib.Path.home()` function looks like:

@classmethod
def home(cls):
"""Return a new path pointing to the user's home directory (as
returned by os.path.expanduser('~')).
"""
return cls(cls()._flavour.gethomedir(None))

If we add a `username=None` parameter and pass this to `gethomedir()` we can 
easily add a lookup of another user's home directory, so:

import pathlib
username = 'phil'
pathlib.Path.home(username) == pathlib.Path('~' + username).expanduser()

--
components: Library (Lib)
messages: 385472
nosy: barneygale
priority: normal
severity: normal
status: open
title: pathlib.Path: add `username` argument to `home()`
type: enhancement

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