PEP 3147 - new .pyc format

Daniel Fetchinson fetchinson at googlemail.com
Wed Feb 3 23:28:14 CET 2010


>>> Python does most of that for you: it automatically recompiles the
>>> source whenever the source code's last modified date stamp is newer
>>> than that of the byte code. So to a first approximation you can forget
>>> all about the .pyc files and just care about the source.
>>
>> True, but the .pyc file is lying around and I always have to do 'ls -al
>> | grep -v pyc' in my python source directory.
>
>
> So alias a one-word name to that :)
>
>
> [...]
>> Here is an example: shared object files. If your code needs them, you
>> can use them easily, you can access them easily if you want to, but they
>> are not in the directory where you keep your C files. They are somewhere
>> in /usr/lib for example, where they are conveniently collected, you can
>> inspect them, look at them, distribute them, do basically whatever you
>> want, but they are out of the way, and 99% of the time while you develop
>> your code, you don't need them. In the 1% of the case you can easily get
>> at them in the centralized location, /usr/lib in our example.
>>
>> Of course the relationship between C source files and shared objects is
>> not parallel to the relationship to python source files and the created
>> pyc files, please don't nitpick on this point. The analogy is in the
>> sense that your project inevitable needs for whatever reason some binary
>> files which are rarely needed at hand, only the
>> linker/compiler/interpreter/etc needs to know where they are. These
>> files can be stored separately, but at a location where one can inspect
>> them if needed (which rarely happens).
>
> I'll try not to nit-pick :)
>
> When an object file is in /usr/lib, you're dealing with it as a user.
> You, or likely someone else, have almost certainly compiled it in a
> different directory and then used make to drop it in place. It's now a
> library, you're a user of that library, and you don't care where the
> object file is so long as your app can find it (until you have a
> conflict, and then you do).
>
> While you are actively developing the library, on the other hand, the
> compiler typically puts the object file in the same directory as the
> source file. (There may be an option to gcc to do otherwise, but surely
> most people don't use it often.) While the library is still being
> actively developed, the last thing you want is for the object file to be
> placed somewhere other than in your working directory. A potentially
> unstable or broken library could end up in /usr/lib and stomp all over a
> working version. Even if it doesn't, it means you have to be flipping
> backwards and forwards between two locations to get anything done.
>
> Python development is much the same, the only(?) differences are that we
> have a lower threshold between "in production" and "in development", and
> that we typically install both the source and the binary instead of just
> the binary.
>
> When you are *using* a library/script/module, you don't care whether
> import uses the .py file or the .pyc, and you don't care where they are,
> so long as they are in your PYTHONPATH (and there are no conflicts). But
> I would argue that while you are *developing* the module, it would more
> nuisance than help to have the .pyc file anywhere other than immediately
> next to the .py file (either in the same directory, or in a clearly named
> sub-directory).

Okay, I think we got to a point where it's more about rationalizing
gut feelings than factual stuff. But that's okay,
system/language/architecure design is often times more about gut
feelings than facts so nothing to be too surprised about :)

Cheers,
Daniel



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