How do *.pyc files execute?

Question

I noticed importing an executable Python file saves a *.py[co] file, as expected, but that file also is marked executable. Randomly, I wondered if I could execute this file directly, and it worked!

Steps to duplicate:

$ echo 'print "Worked."' > testcase.py
$ chmod u+x testcase.py
$ python -c 'import testcase'
Worked.
$ ./testcase.pyc
Worked.

How did this work? Why didn't I get an error message? Is my system, Ubuntu 9.04, doing something special, or am I forgetting something on how Linux works in general?

$ python --version
Python 2.6.2
$ hd testcase.pyc
00000000  d1 f2 0d 0a a4 4f 08 4b  63 00 00 00 00 00 00 00  |.....O.Kc.......|
00000010  00 01 00 00 00 40 00 00  00 73 09 00 00 00 64 00  |[email protected].|
00000020  00 47 48 64 01 00 53 28  02 00 00 00 73 07 00 00  |.GHd..S(....s...|
00000030  00 57 6f 72 6b 65 64 2e  4e 28 00 00 00 00 28 00  |.Worked.N(....(.|
00000040  00 00 00 28 00 00 00 00  28 00 00 00 00 73 0b 00  |...(....(....s..|
00000050  00 00 74 65 73 74 63 61  73 65 2e 70 79 74 08 00  |..testcase.pyt..|
00000060  00 00 3c 6d 6f 64 75 6c  65 3e 01 00 00 00 73 00  |..<module>....s.|
00000070  00 00 00                                          |...|
00000073

(Including hexdump to show there's no shebang line, and reading about .pyc format, there's nothing here that isn't highly specific to Python.)

Solution

Perhaps your system has a binfmt_misc entry for .pyc files. Look in /proc/sys/fs/binfmt_misc for the entry.

Comments

[laurent]

True, but not the question I'm asking. I executed the file and it worked, instead of producing an error. How did that happen?