Multiple versions of Python coexisting in the same OS

[Edward Diener]

On 7/25/2010 4:22 PM, News123 wrote:
> On 07/25/2010 09:33 PM, Edward Diener wrote:
>> On 7/25/2010 10:31 AM, News123 wrote:
>>> On 07/25/2010 02:46 PM, Edward Diener wrote:
>>>> On 7/25/2010 6:07 AM, Gelonida wrote:
>
>>
>> How does a 'pystarter' program know where the file's location is which
>> is being invoked ?
> the file's location would be somewhere in sys.argv
> probably in sys.argv[1].
> converting it to  an abs path would return a directory which the python
> file belongs to.
>
>
>> As to the first file line this is completely
>> unrealistic. What are you going to do, alter the first file line of
>> every script in a Python distribution and every script in every library
>> installed in a Python distribution ? Sorry, but a less intrusive
>> solution is much better and much less of a headache to say the least.
>>
> Well I would at least do it for all of my self written scripts.
>
> It could allow a soft transition from 2.6 to 2.7 to 3.0 without having
> to upgrade all scripts at the same time.

Intrusively changing scripts is a path to Python hell.

>
>> My intended solution would be a simple program which understands where
>> each co-existing Python distribution is installed on a system and what
>> the "name" of that distribution is. Then you tell the program which
>> Python distribution should be the current one by its "name", the current
>> one meaning the distribution which you want to be invoked at any given
>> time. The program then changes the PATH so that any references to the
>> Python directory and its subdirectories point to the "name" Python
>> directory tree, and changes the file associations so that the "name"
>> Python executables handle the Python associations.
>
>
>>
>> This does have the weakness that I can not use more than one Python
>> distribution while Python is executing scripts. But I can personally
>> live with that since I have never encountered a situation where I must
>> use more than one Python distribution at the same time.
>>
>
> I guess it's rather difficult to find a solution which suits all.
>
> The above minor weakness, that you mention would be a killer for me.
>
> Currently I'm looking for solutions, where I can start python scripts
> requireing different python versions at the same time.

If you need that, then of course my intended solution would not work.

>
> Currently I'm staring the scripts manually from two different cmd line
> windows with a different path name and an explicit python call,

If you start scripts and point to a specific version of Python, this 
works in my solution also. But if an internal call to Python exists 
thwre is always a problem.

>
> Thus my idea of having a pystarter with a config file
> mentioning which directories (tools) should use which python executable

Well, good luck ! I don;t know how this is resolved for you when some 
scripts executes 'python xxx yyy' or 'someScript.py yyy'.