[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Eryk Sun]

Eryk Sun  added the comment:

ntpath.expanduser() no longer uses HOME (though the doc string still refers to 
$HOME), so at least that problem is resolved. 

I suppose IDLE could work around the HOME issue in Windows by passing 
env=os.environ.copy() in the subprocess.Popen() call that creates the 
subprocess. os.environ will not contain the HOME value that TCL sets in the 
underlying process environment.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Terry J. Reedy added the comment:

How about wrapping the appropriate tkinter code with (untested yet)

import os
HOME = os.environ['HOME']
try:

finally"
os.environ['HOME'] = HOME  # will this unset?

or use a restore_env('HOME', ...) context manager?

Revising os.expanduser or apps to ignore HOME while tk is running is a related 
but different issue.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Jarrod Petz]

Jarrod Petz added the comment:

eryksun, now I understand this is a bit more challenging because tkinter is the 
underlying library doing this and it is shared by other apps.

Though I still don't feel that just because its been like this since 1995 means 
it should stay this way. This is something which breaks other code following 
the python os.path.expanduser way(and probably other thing looking at the 
evitonmeny HOME). Not all people will try getting to the bottom of why, 
esspecially if they are a new user. It should just work.

Would iy be possible for tkinter to allow the user/app to decide the behavior?

Ie. Have a setting(s)/switch which allows the default behavior of setting and 
using HOME to be overiden.

By doing that existing apps remain unchanged and apps like IDLE could change 
this behavior to whatever they want when they are ready.

I think os.path.expanduser() behavior is by far more logical. Preference 
USERPROFILE if HOME is missing. USERPROFILE on windows is needed to even login. 
HOMEDRIVE/HOMEPATH is not.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[ppperry]

Changes by ppperry :


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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Terry J. Reedy added the comment:

ppperry, when I changed this to a doc issue, I added IDLE back as a component 
because, as I said in my last message, I want to include the facts revealed 
here in the IDLE doc.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[ppperry]

Changes by ppperry :


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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Terry J. Reedy added the comment:

#14576 is more or less about making better use of USERPROFILE when the value 
returned by expanduser to config.IdleConf.GetUserCfgDir fails.  Now that I know 
that tcl always sets HOME (or pieces that are joined back together to make 
HOME), so that expanduser never fails (?), this might make some sense - but 
only if they are not the same.

Zach, I was thinking that _tkinter read TCL_LIBRARY to start tcl, but your 
answer suggests that it is instead read by tcl.

The problem with bad TCL_LIBRARY is that if IDLE is started normally, there is 
no error message.  Even if the user tries starting in the console, the message 
is almost useless.  I "set TCL_LIBRARY=NONE" and got
   ...
  File "C:\Programs\Python35\lib\tkinter\__init__.py", line 1867, in __init__
self.tk = _tkinter.create(screenName, baseName, className, interactive, 
wantobjects, useTk, sync, use)
_tkinter.TclError: Can't find a usable init.tcl in the following directories:
NONE C:/Programs/Python35/lib/tcl8.6 C:/Programs/lib/tcl8.6 C:/lib/tcl8.6 
C:/Programs/library C:/library C:/tcl8.6.4/library C:/tcl8.6.4/library

Everything after NONE is nonsensical.  The IDLE doc needs a new sections "If 
IDLE does not start:.  Now I could write a troubleshooting note explaining for 
this note to ignore everything after the first item, and that the first item is 
an unusable setting of TCL_LIBRARY set by something or someone other than 
Python/Tkinter/IDLE.

I tried the same experiment with TK_LIBRARY and could see no effect.

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components: +Documentation, IDLE
nosy: +docs@python

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Zachary Ware]

Zachary Ware added the comment:

For the original issue, I agree with Eryk that about the best we can do is to 
document that Tcl sets HOME as "%HOMEDRIVE%%HOMEPATH%" or "c:\" if both of 
those are not set.  I wonder about removing (or de-preferring) HOME in 
os.path.expanduser, but that would be a significantly backward incompatible 
change.  Since HOME is not set by default on Windows, setting it is the easiest 
way to manipulate os.path.expanduser, and changing it is going to break things.

The TCL_LIBRARY issue is completely separate.  I rewrote the logic that used to 
be in tkinter._fix for 3.5, it's now a part of _tkinter initialization and 
TCL_LIBRARY is no longer set (permanently) by tkinter (TK_LIBRARY is not set or 
inspected at all anymore, except by Tk itself).  I did this in an effort to 
avoid the environment warnings in the tkinter/IDLE tests, but apparently missed 
the HOME issue at that point.

Anyhow, we could theoretically unset TCL_LIBRARY (and TK_LIBRARY) in that 
initialization code, possibly conditional on whether TCL_VERSION can be found 
in the content of TCL_LIBRARY (the assumption being that a library for the same 
major version of Tcl ought to work anyway).  However, without that conditional, 
that would be another big backward compatibility issue; setting 
{TCL,TK}_LIBRARY is a legitimate way to point tkinter towards a non-standard 
Tcl/Tk library location (e.g. in an embedding situation).  With conditional 
clearing of {TCL,TK}_LIBRARY, we're still at the mercy of a just plain bad 
setting that just happens to contain the magic string that makes it look 
acceptable.

I'm -1 on making such a change anyway.  We've avoided permanently setting 
TCL_LIBRARY for many many years, other applications can figure out how to avoid 
it as well.  We can't try to clean up messes made by other badly behaved 
programs, that way lies madness.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

This is Windows specific issue, I can't help with this, sorry. Zach should be 
more experienced in this.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Terry J. Reedy added the comment:

Python does not set TCL_LIBRARY.  _tkinter finds tcl/tk installed with Python 
at its known location for the platform. tkinter and IDLE work fine for months.  
Then user installs another program. That other software (not user, and 
unbeknownst to the user) sets TCL_LIBRARY to something that _tkinter cannot 
use.  I am guessing that _tkinter, seeing TCL_LIBRARY, tries to use alternate 
install, cannot, and gives up, instead of falling back to the python-tcl it was 
using for months.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

What is the problem? That user sets incorrect TCL_LIBRARY? I don't know how 
_tkinter can distinguish correct TCL_LIBRARY from the incorrect one.

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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Changes by Terry J. Reedy :


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[issue27263] Tkinter sets the HOME environment variable, breaking scripts

[Terry J. Reedy]

Terry J. Reedy added the comment:

As IDLE maintainer, this annoys me also. IDLE and in particular test_idle 
necessarily change the environment by calling tkinter.Tk().  When run under 
test.regrtest, test_idle gets slapped with a warning, and in 3.6, gets labelled 
a failure, even when it passes.

This issue cuts the other way too.  IDLE works for months and then stops 
working.  User posts "IDLE stopped working' on Stackoverflow.  In at least some 
cases, user installed a program that installed ab incompatible tcl/tk and set 
TCL_LIBRARY (which Python does not).  tk and tkinter get trapped by what for us 
is a bad setting.

Serhiy, could the _tkinter startup code recover from this and revert to using 
the one we installed?  Should I open a separate issue?

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components:  -IDLE
nosy: +serhiy.storchaka, terry.reedy
title: IDLE sets the HOME environment variable breaking scripts -> Tkinter sets 
the HOME environment variable, breaking scripts

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