Re: msvcp71.dll and Python 2.4 C++ extensions

From: Matthias Baas (baas_at_ira.uka.de)
Date: 02/01/05

  • Next message: Nick Craig-Wood: "Re: Where are list methods documented?" 
    Date: Tue, 01 Feb 2005 21:26:04 +0100

    On Tue, 01 Feb 2005 00:14:30 +0100, "Martin v. Löwis"
    <martin@v.loewis.de> wrote:
    >> are there any guidelines about what to do if a Windows extension for
    >> Python 2.4 requires the C++ runtime (msvcp71.dll)?
    >
    >No; it should "just work fine". [...]

    I fully agree with that. :) And that was actually the reason why I
    posted here, because in my case it did not just work fine...

    >> It doesn't
    >> sound like a good idea to me if every package places another copy of
    >> this dll somewhere in the Python directory.
    >
    >Why not? If your installer follows Windows logo compliance rules, it
    >should check whether the DLL is already present; if it is, it should
    >check whether the version installed is newer than the one it would
    >install, and if so, should skip installation.

    I'm creating the installer via the distutils by calling "setup.py
    bdist_wininst". How can I configure distutils to have it create an
    installer that does the above things?

    How should an installer check if a DLL is already present? Are DLLs
    registered with Windows so I can query a database? Or should the
    installer search for the DLL in the directories specified in the PATH
    variable and see if the DLL is there?
    And what's the preferred location for such a DLL? Should it be placed
    in a local directory that only belongs to the package or in a
    directory where other C++ extension packages might also be able to use
    it? But where would this be then? The Windows system directory seems
    to be discouraged by Microsoft:

    "An application should use and redistribute msvcr71.dll, and it should
    avoid placing a copy or using an existing copy of msvcr71.dll in the
    system directory. Instead, the application should keep a copy of
    msvcr71.dll in its application directory with the program executable."
    (see
    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclib/html/_crt_c_run.2d.time_libraries.asp)
    I suppose the same applies for msvcp71.dll.

    >> Python 2.4 does install the C runtime (msvcr71.dll) in the Windows
    >> system32 directory, doesn't it?
    >
    >It depends. If this is an allusers installation, it does so. For a
    >per-user installation, the user might not have sufficient privileges
    >to install into system32, so the installer won't install it there.

    Ah, ok. And yes, I did a "all users" installation.

    >> (btw, shouldn't this be installed in
    >> the Python directory instead?)
    >
    >No. If you install the DLL into the Python directory, Python
    >will not work anymore because python24.dll (installed into system32)
    >will not find this DLL. If you then also move python24.dll into
    >the Python directory, COM components that require python24.dll will
    >fail to run.

    ok, I see.

    >> So would it be possible that future
    >> Python releases would also install the C++ runtime?
    >
    >Why should it? Nothing in the Python distribution requires C++.

    Well, yes, I know. But I don't see Python as a standalone application.
    One of the great things about Python is that there are so many
    extension modules for every kinds of purposes. So, making available
    the C++ runtime would just pave the way for more of those extension
    modules by making it easier to distribute binary packages that are
    implemented in C++.

    >> I think it's
    >> better if the dll would only be installed once by Python instead of
    >> several times by every extension that uses C++.
    >
    >Why is that better? The DLL versioning rules, and the shared DLL
    >refcounting mechanisms will make sure that the installation works
    >just fine.

    I was referring to the possibility that the DLL might get installed
    several times at several different locations which would be a waste of
    disk space. If there's only one file, then I agree with the above
    (however, what happens if I uninstall one package and this package
    removes the DLL even when there are other packages installed that
    still require the DLL?).

    >> Currently, I do not package the C++ runtime and leave it up to the
    >> user to install the dll if it isn't already somewhere on his system.
    >> But this really is not a satisfying solution...
    >
    >Then you should probably include the DLL, or rewrite your extension
    >to not use C++.

    I'm afraid the latter will hardly ever be an option... ;)

    For one smaller package I was compiling I solved the problem by
    linking against the static versions of the C/C++ runtime. This will
    also satisfy the "It-Should-Just-Work" constraint... :) (however,
    there still could be situations where this is not possible (the
    sources might not be available, for example)).

    - Matthias -

  • Next message: Nick Craig-Wood: "Re: Where are list methods documented?"

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