Not all of the ideas below are complementary to each other, some are either or, to allow different thoughts to be inspired or different directions to be taken. Thanks for starting a PEP. On 3/18/2011 11:02 PM, Mark Hammond wrote: > The launcher should be as simple as possible (but no simpler.) The launcher could be simpler if it isn't used for launching interactive interpreters as well as script references via Windows associations (more about that after the next quote). The launcher could be simpler if it just read through the file of its first parameter until it finds a line starting with #@ (process as a Windows version of Unix #!) or starting without a # (error case). This avoids the need parse such lines. So in reality, you are not trying to make launcher as simple as possible, but rather attempting to make some perceived usage case simple, and make the launcher more complex (and harder to define, document, and implement) rather than suggesting that since Unix and Windows are different, that maybe they should have different lines in the script to help launch them. Remember, the typical Windows user is not likely to place a #! line in their scripts in the first place, so teaching them what a Unix #! line is, and how the parameter after it should be something that Windows doesn't even use, and the launcher has to work hard to interpret, is not as simple as possible. The launcher could be simpler if the Python installer placed versioned Python executables on the PATH. Unfortunately, historically it hasn't. If it did, would, or the launcher installer would place them there for pre-existing versions of Python, then the launcher could work by launching the appropriate version of Python, expecting Windows to find it on the PATH. The PEP doesn't address the level of internal complexity of the launcher necessary to find where Python has been installed, neither for CPython, nor for the alternate implementations to be supported. The launcher could be simpler if a directory \usr\bin were created under Windows Program Files, placed on the PATH, and %ProgramFiles% prepended to the Unix #! line, with the Python/Jython/Cython installers placing appropriately versioned executables in that directory. Could even start a trend for programs ported from Unix. One could even place an "env" program there, for more simplicity. > * When used to launch an interactive Python interpreter, the launcher > will support the first command-line argument optionally be a > version specifier in the form "-n[.n]" (where n is a single > integer) to nominate a specific version be used. For example, > while "py.exe" may locate and launch the latest Python 2.x > implementation installed, a command-line such as "py.exe -3" could > specify the latest Python 3.x implementation be launched, while > "py.exe -2.6" could specify Python 2.6 be located and launched. > If a Python 2.x implementation is desired to be launched with the > -3 flag, the command-line would need to be similar to "py.exe -2 > -3" (or the specific version of Python could obviously be > launched manually without use of this launcher.) I think that a python launcher that is "on the PATH" that could be used to launch an interactive Python, should be different than one that is used to launch XXXX.py[w] scripts. The above paragraph raises the issues below, which I think are confusing enough to justify this, IMO. Certainly, if the same python launcher is used for both cases, a lot more clarity around parameter handling must be provided. 1) python should be invoked interactively by typing "python" or "pythonX[.Y]" at the CMD prompt, not "py". This can be done without a launcher, if appropriate versioned pythons are placed on the PATH. The launcher is really and only needed for handling XXXX.py[w] scripts, which, in the Windows way of thinking, can only be associated with one specific, system-wide configured version of Python (presently, the latest one wins). The script itself is not examined to modify such an association. The Unix !# line provides such modification on Unix. 2) If the launcher provides command line options for the "benefit" of launching interactive Python interpreters, those command line options can have data puns with script names, or can conflict with actual Python options. I believe Python 2 already has a -3 option, for example. And Windows users are not trained that "-" introduces an option syntax, but rather "/". Most _programmer_ users would probably be aware of "-" as an option syntax, but Python is used as a language for non-programmers in some circles, and few Windows non-programmers understand "/" much less "-" and not even command lines very well. So not using a launcher for launching interactive Python sidesteps all that: Python itself is introduced and taught, and no need to teach about (or even have) launcher options that could possibly conflict and confuse, in addition to Python options that may conflict with script names already. (I have seen lots of Windows users use leading punctuation characters on filenames to affect sort order and grouping of files in My Documents, not knowing they can create subdirectories/subfolders, or not wanting to bother with them, since all their applications default to opening things from My Documents.) 3) Unix !# lines can have embedded options after the program name on the line. Such options would be another source of potential conflict with launcher options, if the launcher has options for use with launching interactive interpreters. Item 3 is also an issue for the PEP even apart from its use as an interactive Python launcher; since options may exist on the Unix #! line, a discussion of how and if they are handled by the launcher should be included in the PEP. > * Environment varialbes will be used to override the semantics for > determining exactly what version of Python will be used. For > example, while a shebang line of "/usr/bin/python2" will > automatically locate a Python 2.x implementation, an environment > variable can override exactly which Python 2.x implementation will > be chosen. Similarly for "/usr/bin/python" etc. Clarify if environment variables can be used to override semantics for shebang lines of the form "/usr/bin/python2.x". > The launcher should be capable of supporting implementations other > than CPython, such as jython and IronPython. In particular, if there > are common symbolic links used on Unix to specify such an > implementation (such as "/usr/bin/jpython", the launcher should > support such references on Windows. However, the launcher on Windows > need not create its own conventions for use on Windows - ie, if > "/usr/bin/jython" is not commonly found on Unix and therefore does > not commonly exist in shebang lines, the Windows launcher need not > support it. The ability to specify the fully-qualified path to the > executable could be used just as it would need to be done on Unix. I am under the impression that IronPython is a Windows-only implementation, but even if it becomes available on Unix via Mono it is certainly possible to have Windows-specific implementations. Apparently the above prevents the launcher from launching a Windows-specific implementation not commonly available on Unix. > A shebang line will be parsed according to the rules in [1]. Once > parsed, the command will be examined to see if it is a "virtual > command". A virtual command starts with either of the 2 strings > '/usr/bin/python' or '/usr/bin/env python'. If alternate implementations are to be supported, additional virtual commands will be required, not just these two. Each one adds complexity to the launcher. > Non-virtual shebang lines should be discouraged as they make the > script specific to a specific Windows installation. However, they > are supported for maximum flexibility. This is a false statement. Non-virtual shebang lines do not make a script specific to a specific Windows installation, only specific to the (often quite large) subset of Windows installations with particular characteristics that are reflected in the non-virtual shebang line. I think the major issue here is whether the Python is installed in drive C: or some other drive letter; a secondary issue would be if reference is made to a 32-bit Python on a 64-bit Windows, which wouldn't port back to a 32-bit Windows not having the "Program Files (x86)" path. Within a corporate environment, the system drive, and the Python installation drive, are likely to be consistent. Outside a corporate environment, most Windows system drives, and most Python installation drives are both C: and references to "C:\Program Files" are highly portable. A Windows #@ could support syntax such as "#@ %ProgramFiles%\python3.2\python.exe" where the %-enclosed syntax would be looked up in the environment (that is a predefined variable on current versions of windows, not sure how far back in history it goes). -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20110319/a3ac3803/attachment-0001.html>
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