Only Bytecode, No .py Files

Christian Heimes lists at
Wed Jul 27 05:27:33 EDT 2011

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 =
>>> 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

>>> open("", "w").close()

Set its mtime

>>> os.utime("", (mtime, mtime))

Now the 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.


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