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Re^3: Perl: friend or foe ?

by skyknight (Hermit)
on Apr 24, 2005 at 14:19 UTC ( #450968=note: print w/replies, xml ) Need Help??


in reply to Re^2: Perl: friend or foe ?
in thread Perl: friend or foe ?

I'm worried that if I mention Python one more time this weekend I might get dragged off by a lynch mob, but here goes anyway... When you import a module in Python, say module Foo.py, it writes to disk the byte code of the compilation in a file called Foo.pyc. The next time you run, it goes to do the same thing, but checks the time stamps on the .py file and .pyc file, only recompiling the .pyc file if it is stale, and otherwise just reading it in and ignoring the .py file. There are no Makefiles involved.

What is wrong with this idiom? I guess one tricky issue is where you put the .pyc files. If you don't have permission to the directory in which the .py files are stored, and the .pyc files aren't already there, then I suppose you have to figure out where to put the .pyc files you create, though I don't think this would be too terrible. You could have a python cache directory in your home directory, or something like that.

Why wouldn't such an idiom work for Perl?

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Re^4: Perl: friend or foe ?
by merlyn (Sage) on Apr 24, 2005 at 14:40 UTC
    To be able to do that in Python, you have to give up source filters and prototypes in Perl. If you want no source filter or no prototypes, you know where to find Python, but I prefer that they stay in Perl.

    If you want to promise never to use prototypes or source filters (or any module that might use those), you can certainly use B::Bytecode to create compiled ".pmc" files. In fact, I think the current "use" operator already probes for .pmc as well as .pm files.

    -- Randal L. Schwartz, Perl hacker
    Be sure to read my standard disclaimer if this is a reply.


    Update: regarding .pmc files: seen in perldoc -tf require:
    Now that you understand how "require" looks for files in t +he case of a bareword argument, there is a little extra functionality going on behind the scenes. Before "require" + looks for a ".pm" extension, it will first look for a filename w +ith a ".pmc" extension. A file with this extension is assumed to + be Perl bytecode generated by B::Bytecode. If this file is fo +und, and it's modification time is newer than a coinciding ".pm +" non-compiled file, it will be loaded in place of that non-compiled file ending in a ".pm" extension.
Re^4: Perl: friend or foe ?
by perrin (Chancellor) on Apr 24, 2005 at 16:59 UTC
    I think the bottom line is that mod_perl and similar daemonizing tools (PPerl) makes all this work totally unnecessary. If those didn't exist, people would likely be a lot more interested in saving the in-between steps.
Re: Perl: friend or foe ?
by MonkPaul (Friar) on Apr 24, 2005 at 14:29 UTC
    Ah, now we have hit the nail on the head.

    If pyton looks at the previous code and its time stamp etc, and other languages complie their code also, then surely this is an advantage if the program code is big and has lots of intergrated snipptes from other modules.
    Yet, with perl, its runtime compilation makes it far quicker than the 'compliers' for small programs.

    Can a middle man language be concieved, where, for instance it has the option of compiling the code again if its a large program, or performing a runtime execution.

Re^4: Perl: friend or foe ?
by bart (Canon) on Apr 24, 2005 at 20:06 UTC
    I seem to recall of some tests that tried this approach for perl, and that the resulting binary was so huge, that it turned out that recompiling perl from source was actually faster, than loading this huge binary from disk.

    Can anybody confirm or deny this anecdote?

Re^4: Perl: friend or foe ?
by chromatic (Archbishop) on Apr 24, 2005 at 20:38 UTC

    Timestamps fail too often for Makefiles. If there's another comparison possibility, such as hashing the original source file and storing that in a header of the compiled file, it could be useful.

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