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To: python-list@python.org
From: Christian Heimes <lists@cheimes.de>
Subject: Re: Only Bytecode, No .py Files
Date: Wed, 27 Jul 2011 00:04:07 +0200
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10349

Am 26.07.2011 23:20, schrieb Eldon Ziegler:
> That seemed like a good idea but the .py file was complied even though
> it was dated 2001-01-01 00:00:00. Python must be checking something
> beside the date.

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.

Hint: If you run python with the -v option, you can get information why
a pyc file is ignored.

$ touch test.py
$ pycompile test.py
$ python -v -c "import test"
...
# test.pyc matches test.py
import test # precompiled from test.pyc
...
$ touch test.py
$ python -v -c "import test"
...
# test.pyc has bad mtime
import test # from test.py
...

Christian