[issue17010] Windows launcher ignores active virtual environment

[Vinay Sajip]

Vinay Sajip added the comment:

> Is there any discussion which lead to this change?

http://mail.python.org/pipermail/python-dev/2013-May/125939.html

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[issue17010] Windows launcher ignores active virtual environment

[Piotr Dobrogost]

Piotr Dobrogost added the comment:

@Vinay
Is there any discussion which lead to this change?

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[issue17010] Windows launcher ignores active virtual environment

[Vinay Sajip]

Changes by Vinay Sajip :


--
resolution:  -> fixed
status: open -> closed

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[issue17010] Windows launcher ignores active virtual environment

[Vinay Sajip]

Vinay Sajip added the comment:

Recent changes to the launcher mean that for a shebang line of "#!/usr/bin/env 
python", the path is searched for a Python executable. This will include the 
Python executable in an activated venv, so I am closing this issue. The change 
is already available for testing in the standalone launcher at

https://bitbucket.org/pypa/pylauncher/downloads/

and should be incorporated into the launcher released with Python 3.4.

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[issue17010] Windows launcher ignores active virtual environment

[Piotr Dobrogost]

Piotr Dobrogost added the comment:

Issue titled "Python Launcher and virtualenv?" at 
https://bitbucket.org/vinay.sajip/pylauncher/issue/15/ is related.

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nosy: +piotr.dobrogost

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[issue17010] Windows launcher ignores active virtual environment

[Vinay Sajip]

Vinay Sajip added the comment:

When using an activated virtual environment, there is no need to use "py" - 
just use "python". Primarily, the launcher looks for a shebang line in a script 
to determine which interpreter to use for the script. If no shebang line can be 
found, it will launch "the default" Python, which is currently the most recent 
Python 2.x found in the registry. When invoked via py -3 (or with suitable 
settings in the configuration), it will use the most recent Python 3.x found in 
the registry. Since venv interpreters are not in the registry, they will never 
be invoked as the default Python. However, any scripts installed into venvs 
will have the correct shebang lines, so they will launch with the venv's 
interpreter.

I don't believe this is a bug, as the system is IMO working as designed and as 
per PEP 397. If the launcher is asked to launch a script which contains a 
shebang, while a venv is activated, it will run with the interpreter indicated 
by the shebang, rather than the venv's interpreter.

Perhaps one could consider an enhancement whereby if no shebang is found, a 
different approach is used to find the interpreter - e.g. looking for "python" 
on the path before looking in the registry to locate an interpreter. The 
question arises as to whether this should be tied to a specific condition such 
as the presence of an environment key PYLAUNCHER_USEPATH. (This is of course 
orthogonal to whether or not a venv is activated, but would have the desired 
effect when a venv is activated, without needing to tie the launcher to a 
virtualenv-specific environment value such as VIRTUAL_ENV.)

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[issue17010] Windows launcher ignores active virtual environment

[Éric Araujo]

Changes by Éric Araujo :


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components: +Interpreter Core -Installation
nosy: +brian.curtin, tim.golden, vinay.sajip
stage:  -> needs patch
versions: +Python 3.4

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[issue17010] Windows launcher ignores active virtual environment

[Bryan G. Olson]

New submission from Bryan G. Olson:

Python 3.3 includes PEP 397, a Python launcher for Windows, and PEP 405, 
virtual environment support in core. Unfortunately the Windows launcher does 
not respect virtual environments. Even with with a virtual environment 
activated and the current directory at the virtual environment's root, the 
Windows launcher will start python with the system environment, not the active 
virtual environment.


To demo:

Install python 3.3 for windows.

Create a virtual environment:

  C:\>c:\Python33\Tools\Scripts\pyvenv.py c:\virtpy

Activate the virtual environment:

  C:\>virtpy\Scripts\activate.bat
  (virtpy) C:\>

Optionally cd to the virtual environment:

  (virtpy) C:\>cd virtpy
  (virtpy) C:\virtpy>

Start Python 3 with the new windows launcher:

  (virtpy) C:\virtpy>py -3
  Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:55:48) [MSC v.1600 32 bit 
(Intel)] on win32
  Type "help", "copyright", "credits" or "license" for more information.
  >>>

Check sys.path

  >>> import sys
  >>>
  >>> sys.path
  ['', 'C:\\Windows\\system32\\python33.zip', 'C:\\bin\\Python33\\DLLs', 
'C:\\bin\\Python33\\lib', 'C:\\bin\\Python33', 
'C:\\bin\\Python33\\lib\\site-packages']
  >>>


The worst effect I've found is that installation of a package with windows 
launcher, "py -3 setup.py install", will ignore the active virtual environment 
and will change the system Python environment. That's bad because users 
frequently employ virtual environments to isolate changes that could damage a 
system configuration.

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components: Installation, Windows
messages: 180362
nosy: bryangeneolson
priority: normal
severity: normal
status: open
title: Windows launcher ignores active virtual environment
type: behavior
versions: Python 3.3

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