[Chicago] exec saved compiled code

[Massimo Di Pierro]

Thank you, this is very helpful!

Massimo

On Aug 29, 2007, at 9:20 AM, Atul Varma wrote:

> I believe you may want to use marshal instead of pickle.  In fact,
> .pyc files are actually just marshalled code objects with a bit of
> header information at the front--specifically, a 4-byte "magic number"
> followed by a last-modified-timestamp of the source .py file.
>
> Going back to your original example, loading a .pyc file can be  
> done like so:
>
>   # Compile the .pyc file (this is unchanged from your original post)
>   environment={'x':3}
>   open('a.py','w').write('print x')
>   import py_compile,os
>   exec(open('a.py','r').read()) in environment ### prints 3 OK!
>   py_compile.compile('a.py')
>   os.unlink('a.py')
>
>   # Now load the .pyc file.
>   f = open( "a.pyc", "rb" )
>   pycData = f.read()
>   f.close()
>
>   # Optional: read the magic number and ensure that it's what we  
> expect
>   # for our version of Python.
>   import imp
>   magic = pycData[:4]
>   assert magic == imp.get_magic()
>
>   # Optional: Get the last modified time of the original .py source,
> to tell if we're in
>   # sync with the compiled version of the latest version of the .py
> file.  At least,
>   # that's what I *think* this is for...
>   mtime = pycData[4:8]
>   # Well, actually, we can't do any comparison because we've  
> deleted the
>   # original .py file, so scratch that. :)
>
>   # Read the actual marshalled code object and unmarshal it.
>   codeBytes = pycData[8:]
>   code = marshal.loads( codeBytes )
>
>   # execute the code.
>   exec code in environment
>
> Note that more needs to be done in that last step if you actually want
> to set up a real module (e.g., if you're creating a custom
> importer--see PEP 302 for more information).
>
> It's also interesting to note that the .pyc file format isn't
> documented in prose anywhere, so the following source code can be used
> to determine it:
>
>   http://svn.python.org/projects/python/trunk/Python/import.c
>
> I hope this is helpful.
>
> - Atul
>
> On 8/29/07, Massimo Di Pierro <mdipierro at cti.depaul.edu> wrote:
>>
>> almost... but I want to be able to save c and reload it before the  
>> exec. It
>> appears c cannot be picked.
>>
>> Massimo
>>
>>
>> On Aug 29, 2007, at 2:28 AM, Cosmin Stejerean wrote:
>> I'm not sure if I understand what's going on with the environment  
>> = {} part
>> so I'm not sure if my solution to your problem is correct but here  
>> is what I
>> think is wrong. As far as I can tell exec can take either a string  
>> or a code
>> object. exec(open(' a.py','r').read()) works because you are  
>> reading the
>> code from a file (it could have been any other file extension) and  
>> exec is
>> parsing it.
>>
>> exec(open('a.pyc','r').read()) this however reads the bytecode as  
>> a string
>> and passes it to exec. This is probably not what you want (and  
>> most likely
>> won't work). One solution is to simply import a, but I'm guessing  
>> that's not
>> what you want either. The other option is to not use py_compile  
>> but use the
>> compile function and pickle as follows
>>
>> c = compile("print x", '<string>', 'exec')
>>
>> now you have a code object that you can execute
>>
>> exec(c)
>>
>> If you pickle this code object to a file you will be able to read  
>> it and run
>> it (then again why not pickle the original string??). The problem  
>> is pickle
>> won't pickle code objects. But apparently you can use a little  
>> trick around
>> that (see
>> http://mail.python.org/pipermail/python-list/2002-August/161661.html)
>>
>> Is this at least close to what you were looking for?
>>
>> - Cosmin
>>
>> On 8/29/07, Massimo Di Pierro <mdipierro at cti.depaul.edu > wrote:
>>>
>>> Hello,
>>>
>>> I am hoping one of you can help me with this.
>>>
>>> EXAMPLE:
>>>
>>> environment={'x':3}
>>> open('a.py','w').write('print x')
>>> import py_compile,os
>>> exec(open('a.py','r').read()) in environment ### prints 3 OK!
>>> py_compile.compile(' a.py')
>>> os.unlink('a.py')
>>> exec(open('a.pyc','r').read()) in environment ### does not work
>>>
>>> QUESTION: how do exec a.pyc into environment so that it prints 3? Is
>>> it possible to do it?
>>>
>>> Massimo
>>> _______________________________________________
>>> Chicago mailing list
>>> Chicago at python.org
>>> http://mail.python.org/mailman/listinfo/chicago
>>>
>>
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