[Python-Dev] [PEPs] Support the /usr/bin/python2 symlink upstream

[Michael Foord]

On 06/03/2011 02:33, Mark Hammond wrote:
> On 6/03/2011 12:37 AM, Michael Foord wrote:
>> On 05/03/2011 07:02, Nick Coghlan wrote:
>>> On Sat, Mar 5, 2011 at 10:47 AM, Mark
>>> Hammond<mhammond at skippinet.com.au> wrote:
>>>> I think this discussion should be divorced from this PEP and taken up
>>>> with
>>>> the discussion about the PATH and the "last installed wins" issue 
>>>> Martin
>>>> mentions - only all of them taken together will "fix" this issue -
>>>> not that
>>>> I personally consider it particularly broken - more like
>>>> "sub-optimal" :)
>>> I updated the draft PEP, explicitly bringing Mac OS X and Cygwin
>>> within the scope of the recommendation, and excluding PYTHON*
>>> environment variable considerations and Windows-related proposals. The
>>> Windows section does include a hit-list that may serve as a useful
>>> starting point if someone else felt like starting a Windows specific
>>> PEP, though.
>>
>> The issues are relevant to Windows (there are *other* issues as well but
>> that doesn't mean that the same issue doesn't apply). Guido also said he
>> would like to see Windows addressed.
>
> What issues specifically?  If I look at the current PEP language, it 
> refers to "the default version of the Python interpreter" and "all new 
> code that needs to invoke the Python interpreter".  Neither of these 
> apply in any meaningful way to Windows. 
People often invoke the Python interpreter from the command line to run 
code on Windows.

> It could be argued that the latter could include .bat files which use 
> Python but that sounds like a theoretical problem (ie, I haven't heard 
> much noise about that) where PEP394 is addressing an observed 
> practical problem.
I have my Python installs on my PATH (as do most Windows developers I 
know) and absent batch files I create myself I have no way of 
distinguishing between Python 2 and Python 3 (or other versions) because 
the Windows installer only creates "python.exe".

>
> On Windows it seems to be just about 'python2' and 'python3' doing the 
> correct thing in a default command prompt, which while desirable 
> ignores the broader issues (eg, the file associations and anything 
> else "windowsy" and not driven by the command-prompt)
>

I'm glad it is desirable. Yes there are other issues, yes they should be 
addressed, but not as part of this PEP.
>
>> I'll be happy to try and come to some consensus with Martin (and others)
>> on what we *can* do for Windows (as similar to the other platforms as
>> possible would be my goal) and provide appropriate text for the PEP.
>
> IIUC, the PEP language is referring to links which point to a specific 
> version of Python and that there is no suggestion a 'python3' will 
> live in the Python 3 binary tree.  If that is correct and assuming we 
> don't want to investigate using links on Windows, I'd suggest the best 
> analogy to the *nix situation could be simply for the installers to 
> generate "python2.bat" and "python3.bat" files and put them in 
> System32 with a "last installed wins" policy.  The fact this doesn't 
> help users installing Python "just for me" is fine too from the POV of 
> matching *nix systems - a user installing a private Python build on 
> *nix also doesn't get the python2 and python3 conveniences, nor the 
> automatic PATH convenience.  But in practice I expect this would *not* 
> be OK - which just highlights the risks of trying to generalize a 
> specific observed problem on one OS to others.
>
bat files are far from ideal for the reasons that others have expressed. 
I would like to see us create version specific (i.e. python32.exe / 
python32w.exe) binaries (or links if we drop support for earlier 
versions of Windows or some filesystems - I'm agnostic on that issue) 
*plus* a python3.exe / python3w.exe with "last install wins" (as it is 
for currently for file associations).

Whether we make those "automatically available" by installing into 
System32 or do that later by allowing the installer (optionally) to add 
a PATH entry I don't mind.

Martin seems not to mind this idea and Paul Moore is +1 and Guido would 
like Windows at least addressed by the PEP, so I would *like* this added 
to the PEP unless there is substantial opposition to us doing this.

All the best,

Michael Foord
> Cheers,
>
> Mark


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