Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: Christian Heimes <lists@cheimes.de>
Subject: Re: Only Bytecode, No .py Files
Date: Wed, 27 Jul 2011 11:27:33 +0200
References: <1311693548.3796.212.camel@ewzdev.atlantic>	<CAGGBd_rmMyNdqaokHF5aOtC-YS3xjjW83q1-5dQz=wF31NbNbg@mail.gmail.com>	<1311715229.3796.224.camel@ewzdev.atlantic>	<mailman.1512.1311717864.1164.python-list@python.org> <TUJXp.106882$8G4.66955@newsfe17.iad>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110617 Lightning/1.0b2.102ipre2 Thunderbird/3.1.11
In-Reply-To: <TUJXp.106882$8G4.66955@newsfe17.iad>
OpenPGP: id=AD16AB1B; url=http://cheimes.de/heimes.asc
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1530.1311758872.1164.python-list@python.org>
Lines: 42
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10379

Am 27.07.2011 03:32, schrieb harrismh777:
> Christian Heimes wrote:
>> The first four bytes of a pyc file contain the magic header. It must
>> match the magic of the current Python version. The next four bytes
>> contain the pyc_mtime. It must match the mtime of the corresponding .py
>> files as returned by fstat().st_mtime. If the magic doesn't match or the
>> mtime header doesn't match the mtime of the .py file, the pyc is ignored.
> 
>     ... so recompile is required to fix.

It's not required, you can fake a .py file with a trick:

>>> import os, struct, datetime

First get the magic and mtime from the pyc file

>>> with open("test.pyc", "rb") as f:
...     header = f.read(8)
...
>>> magic, mtime = struct.unpack("ii", header)
>>> magic, mtime
(168686339, 1311717735)

Verify it's a good date

>>> datetime.datetime.fromtimestamp(mtime)
datetime.datetime(2011, 7, 27, 0, 2, 15)

Now create an empty test.py

>>> open("test.py", "w").close()

Set its mtime

>>> os.utime("test.py", (mtime, mtime))

Now the test.py has the same mtime as test.pyc and Python won't
recompile the .pyc file from the .py file as long as the magic header
(168686339) is correct.

Christian