[Python-Dev] [PEPs] Support the /usr/bin/python2 symlink upstream (original) (raw)

Glenn Linderman v+python at g.nevcal.com
Wed Mar 9 08:20:53 CET 2011

On 3/8/2011 10:27 PM, Mark Hammond wrote:

On 9/03/2011 5:05 PM, Glenn Linderman wrote:

Standard installation paths are accepted by about 99% of the users, so embedding standard installation paths can work well for that batch of users. Of course, Windows changes the standard path periodically, so that it different from versions prior to and including WinXP versus versions after WinXP. And they had no standard before WinNT (or if they did, few followed it). Your comment does point out a possible need for multiple standard installation paths just for different versions of Windows, though :( The python installer ignores "Program Files" - as much as anything I'm concerned about the drive letter - IIUC, Python will default to installing on the system drive, which may not be C:

The system drive usually is C:, there is a fair bit of software that won't work when it is not C:, and in any particular corporate environment it is usually standardized by the IT folks. And you are referring specifically to the CPython installer as the IronPython (for example) does install in Program Files.

...

Your premise that using a standard installation path in #@ restricts the script to be targeted to one machine is fallacious, so the conclusions are also. Sorry - I should have said "some machines with Python installed by the installer". Contrast this to the option of looking up the registry and you have "all machines with Python installed by the installer". I'm not going to quibble about the percentages in the first category as I have no data to guide me, but I'm reasonably confident about the "all" in the second. ... The #! line is clearly is NOT "the only clue Windows needs to make it work automagically" or we wouldn't be having this discussion at all. Sorry - I should have been clear - I meant "the only clue a windows specific Python launcher needs".

Sorrier yet :) I think you really meant "the only clue a Windows specific CPython specific Python launcher needs.

> And it is not at all clear if a Windows machine contains Jython, IronPython, and Cython which one should be launched by a launcher. I think it is reasonably clear: it would be the same version which would be launched on most *nix systems. Are there any systems where "/usr/bin/python" would use Jython, for example?

I have no idea the answer to your question... I don't think you do either. There may be some. The sysadmin can change what /usr/bin/python points to. I have seen plenty of Unix systems where /bin/sh is really bash, for example, so if the replacement is "compatible enough" the sysadmin may choose to make such a change.

You could, of course, argue that python-dev is only concerned with CPython, and the launcher can be specific to CPython, and that argument might carry the day, but the CPython registry lookup necessary to make that happen doesn't help the users of alternate implementations a bit, forcing each of them to implement their own launcher as well... I'd have no problem with the Windows launcher supporting other implementations - I expect something like "/usr/bin/jython" would be reasonable. How we locate the installed jython is indeed an interesting problem, but I'd guess it is surmountable - especially if we can get the buy-in of these alternate implementations for their future releases.

Indeed. But now you have a script that require jython on all machines that it runs on, rather than being flexible in being configurable to use the preferred implementations of a particular environment (perhaps CPython 2.6 on Unix boxes, and Jython 2.5 on Windows boxes, or vice versa).

#!/usr/bin/env python2.6 #@"C:\Program Files\Env.exe" ipy2.6.3.exe As above, the C: assumes Windows is installed on C: - that may be common, but not universal. Further, a 64bit machine would probably want "\Program Files (x86)" (which is becoming more and more common)

Yes, same C: issue as above, see response above. And if the launcher comes in a 64-bit version for 64-bit machines, then it would be installed as C:\Program Files\Env.exe on the 64-bit machines. That should be straightforward to achieve.

in .py files and #!/usr/bin/env python2.6 #@"C:\Program Files\Env.exe" ipy2.6.3w.exe in .pyw files. I'm slightly skeptical about that - .pyw files are surely rare on *nix systems and as we've discussed, pyw files are generally not meant to be cmd-line scripts. IOW, I'm skeptical scripts exist which are meant to work with '/usr/bin/env python2.6' on *nix and pythonw.exe on windows.

Indeed, .pyw files are even rare on my Windows box :)

A GUI sort of Python script would generally want to be .pyw on a Windows box. There are a variety of cross-platform GUIs such as Qt and wxWindows, so those same scripts could be written to work on Unix boxes also. Unix, happily, doesn't care about the name of the script as long as the #! line points the right place, and neither does CPython on Unix, at least for non-module scripts (which are the ones that have #! lines anyway). So it is quite conceivable, even if you have never done it personally.

...

So no matter what is done, it won't solve world hunger. Probably that's why Windows users have been left high and dry for years in this regard... there is no "system" Python on it, out of the box, so the only users are those that are smart enough to download and install and configure things, and those who use a Python embedded into an application, at the cost of a Python installation per application, because there has been no "system" Python, and because Windows users are not perceived to be capable of, or willing to bother with, downloading and installing various requisite dependencies.

The resulting vacuum has been filled by people with different points of view, because there has been no technique implemented, none declared to be "best", and anarchy and variant workarounds have abounded. I'm glad solving world hunger is out of scope for this :) I understand your position but my personal opinion is that simple support for #! is more desirable. I'd be happy to go with the consensus though...

The solution should be as simple as possible, but no simpler. -- Albert

I agree that parsing #! for a version and looking that up in the CPython registry entries would help in the limited circumstances where only the CPython implementation is of interest, and the same versions are available with the same names on all the machines of interest to the script.

Of course, my web host has /usr/bin/python (CPython 2.4.2),
/usr/bin/python2.4 (Cpython 2.4.2) and /usr/bin/python (Cpython 2.6 -- apparently 2.6.0). So when I choose the first, I get whatever the sysadmin chooses for that (they are slow to make changes for compatibility reasons, which is good). When I choose the second for my #! line I get 2.4.2 there. Now if I have all of 2.4, 2.4.1, 2.4.3, and 2.4.4 versions installed on my Windows box, which one should be run in the case of /usr/bin/python2.4? The registry doesn't seem to tell which was installed first, second, or last. Should it pick the newest, or the exact match of 2.4? It can hardly intuit which version is most compatible with the other machines I run it on. Whatever is picked would seem to be some heuristic. And what if there is only 2.5 on the Windows boxes? Or what if there is no CPython on the Windows box, but only Jython or IronPython, etc. the heuristics would have to understand all those mappings between versions... or simply not work at all, with no fallback technique to help it work.

With the #@ idea, application installers could ask which version of Python the application should be configured to use, from among the installed versions that the application has been tested with, and update the #@ lines, and that would stay constant for the life the application (and if the application has an installer that is that smart, it also wouldn't need a #! line, likely, when installed for Windows). If there is no installer, then the user (or his sysadmin) must be smart enough to know how to use a text editor, and configure the version he wants by putting its path in the #@ line... and if the user (or his sysadmin) wants to use it cross-platform, then they put in the appropriate #! line for their Unix machines too.

Some configuration for the launcher would be required to handle the case where there is no #! line, or else in those cases, the launcher could report "no #@ line" like Unix's shell reports "syntax error" for python scripts handed to /bin/sh because the #! line was omitted. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20110308/7f4e9bdd/attachment-0001.html>

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