Python version changes, sys.executable does not

J

Jeffrey Froman

Hello All,

I have two python versions installed, one in /usr/bin, and one in
/usr/local/bin. However, when invoking python without a full path,
I get the wrong executable with the right sys.executable string!
----------------------------------------------------------------------------
[root@M1 ~]# ls -l /usr/local/bin/python*
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python2.5
-rwxr-xr-x 1 root root 1281 Jul 19 09:16 /usr/local/bin/python2.5-config
lrwxrwxrwx 1 root root 16 Jul 19 09:16 /usr/local/bin/python-config -> python2.5-config

[root@M1 ~]# ls -l /usr/bin/python*
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python
lrwxrwxrwx 1 root root 6 Jul 18 12:20 /usr/bin/python2 -> python
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python2.3

[root@M1 ~]# which python
/usr/local/bin/python

[root@M1 ~]# /usr/local/bin/python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# env python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.3.4 (#1, May 2 2007, 19:26:00)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]
Traceback (most recent call last):
File "<string>", line 1, in ?
NameError: name 'set' is not defined
---------------------------------------------------------------------------------


On a different machine, with same setup (as far as I can tell), I get the expected
results:
---------------------------------------------------------------------------------
[root@M2 ~]# /usr/local/bin/python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# env python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# python -c "import sys; print sys.executable; print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]
---------------------------------------------------------------------------------

Can anyone tell me what might be causing the erroneous behavior in the first example?

Thanks,
Jeffrey
 
J

Jim Langston

Jeffrey Froman said:
Hello All,

I have two python versions installed, one in /usr/bin, and one in
/usr/local/bin. However, when invoking python without a full path,
I get the wrong executable with the right sys.executable string!
----------------------------------------------------------------------------
[root@M1 ~]# ls -l /usr/local/bin/python*
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python2.5
-rwxr-xr-x 1 root root 1281 Jul 19 09:16
/usr/local/bin/python2.5-config
lrwxrwxrwx 1 root root 16 Jul 19 09:16
/usr/local/bin/python-config -> python2.5-config

[root@M1 ~]# ls -l /usr/bin/python*
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python
lrwxrwxrwx 1 root root 6 Jul 18 12:20 /usr/bin/python2 -> python
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python2.3

[root@M1 ~]# which python
/usr/local/bin/python

[root@M1 ~]# /usr/local/bin/python -c "import sys; print sys.executable;
print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# env python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.3.4 (#1, May 2 2007, 19:26:00)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]
Traceback (most recent call last):
File "<string>", line 1, in ?
NameError: name 'set' is not defined
---------------------------------------------------------------------------------


On a different machine, with same setup (as far as I can tell), I get the
expected
results:
---------------------------------------------------------------------------------
[root@M2 ~]# /usr/local/bin/python -c "import sys; print sys.executable;
print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# env python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]
Click to expand...

I think it's because your python directory is in the path before your
python2.5 directory.
 
J

Jim Langston

Jeffrey Froman said:
Hello All,

I have two python versions installed, one in /usr/bin, and one in
/usr/local/bin. However, when invoking python without a full path,
I get the wrong executable with the right sys.executable string!
----------------------------------------------------------------------------
[root@M1 ~]# ls -l /usr/local/bin/python*
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python
-rwxr-xr-x 2 root root 3783810 Jul 19 09:15 /usr/local/bin/python2.5
-rwxr-xr-x 1 root root 1281 Jul 19 09:16
/usr/local/bin/python2.5-config
lrwxrwxrwx 1 root root 16 Jul 19 09:16
/usr/local/bin/python-config -> python2.5-config

[root@M1 ~]# ls -l /usr/bin/python*
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python
lrwxrwxrwx 1 root root 6 Jul 18 12:20 /usr/bin/python2 -> python
-rwxr-xr-x 2 root root 5396 May 2 16:28 /usr/bin/python2.3

[root@M1 ~]# which python
/usr/local/bin/python

[root@M1 ~]# /usr/local/bin/python -c "import sys; print sys.executable;
print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# env python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Jul 19 2007, 09:13:48)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]

[root@M1 ~]# python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.3.4 (#1, May 2 2007, 19:26:00)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-8)]
Traceback (most recent call last):
File "<string>", line 1, in ?
NameError: name 'set' is not defined
---------------------------------------------------------------------------------


On a different machine, with same setup (as far as I can tell), I get the
expected
results:
---------------------------------------------------------------------------------
[root@M2 ~]# /usr/local/bin/python -c "import sys; print sys.executable;
print sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# env python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]

[root@M2 ~]# python -c "import sys; print sys.executable; print
sys.version; set()"
/usr/local/bin/python
2.5 (r25:51908, Feb 8 2007, 16:29:18)
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)]
Click to expand...

er, of course I meant python2.3 before python2.5
 
J

Jeffrey Froman

Jim said:
I think it's because your python directory is in the path before your
python2.5 directory.
Click to expand...

Thanks for the tip. In fact, /usr/local/bin/python (2.5) is on my PATH
before /usr/bin/python (2.3).

I did find the problem however -- it turns out that caching the executable
path is a feature of the bash shell, possibly a buggy one. After installing
the new executable in /usr/local/bin, bash claimed to be running that
executable, but was actually invoking the cached "python"
at /usr/bin/python.

What sorted out the confusion for me was when someone demonstrated to me how
sys.executable could be fooled:

$ exec -a /usr/bin/foobar python
Python 2.5.1 (r251:54863, May 4 2007, 16:52:23)
[GCC 4.1.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.'/usr/bin/foobar'

To remove the cached version, I ran:
$ hash -d python

After which, running "python" invoked a properly named /usr/local/bin/python
as expected.


Thanks,
Jeffrey
 

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