[Tutor] chain gangs revolt, film at 11

[Danny Yoo]

On Mon, 18 Aug 2003, Kirk Bailey wrote:

> problem,, quoting from the error log:
>
> Traceback (innermost last):
>    File "/www/www.tinylist.org/cgi-bin/wikinehesaed2.py", line 24, in ?
>      os.execl(path+'/wikinehesa.py/'+pagename)
>    File "/usr/local/lib/python1.5/os.py", line 169, in execl
>      execv(file, args)
> OSError: [Errno 20] Not a directory
>
> Path is functioning flawlessly- see script listing to see how it is generated.


Hi Kirk,


A certain Tao verse comes to mind:


"""The wise programmer is told about Tao
and follows it.  The average programmer
is told about Tao and searches for it.
The foolish programmer is told about Tao
and laughs at it.

If it were not for laughter, ther would be no Tao.

The highest sounds are hardest to hear.
Going forward is a way to retreat.
Great talent shows itself late in life.
Even a perfect program still has bugs.

The Tao is hidden beyond all understanding.
"""


The penultimate sentence is one I take to heart.  *grin*


It's human nature to err, and it's not shameful to acknowledge that our
understanding about our programs is less than perfect.  Going in with eyes
closed to certain possibilities might help us find a bug more quickly...
or it may lead us totally astray.  Let's see what we can do to diagnose
the problem without making too many assumptions.


First, it seems that execl() is having a hard time getting at the
executable it's trying to execute.  we should try checking to see if the
path that we're feeding into execl refers to a real file.  We can check
this by adding an assertion:

    complete_path = path + '/wikinehesa.py/' + pagename)
    assert os.path.exists(complete_path), ("file %s does not exist" %
                                           complete_path)
    os.execl(complete_path)


... ok, wait a minute.  If we take a closer look at the error message:

> Traceback (innermost last):
>    File "/www/www.tinylist.org/cgi-bin/wikinehesaed2.py", line 24, in ?
>      os.execl(path+'/wikinehesa.py/'+pagename)
>    File "/usr/local/lib/python1.5/os.py", line 169, in execl
>      execv(file, args)
> OSError: [Errno 20] Not a directory


we can guess that Python is trying to say: "I don't know about a directory
called path+'/wikinehesa.py/'+pagename."  It's very likely that Python is
treating 'wikinhesa.py' as part of a path name.


Are you sure the path to your executable should include 'wikinehea.py/' +
pagename?  I think you mean to ask the system to evaluate 'wikinehesa.py',
using pagename as an an additional argument to the 'wikinehesa.py'
program.  If so, then

    path + "/wikinehesa.py"

alone needs to be our executable argument.


If so, then we need to specity 'pagename' as part of the additional
parameters to execl().  Here is an example that execl()'ing a call to the
'ls' file listing utility:

###
[dyoo at tesuque dyoo]$ python
Python 2.2.1 (#1, Sep  3 2002, 14:52:01)
[GCC 2.96 20000731 (Red Hat Linux 7.3 2.96-112)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.execl('/bin/ls', '/bin/ls', '/home/dyoo/pubsearch')
build		       HACKING		  log
build.xml	       HISTORY		  maint
build.xml.~1.56.~      images		  program.properties
ChangeLog	       index.jsp	  program.properties~
ChangeLog.bak	       index.jsp.~1.16.~  program.properties.backup
css		       INSTALL		  program.properties.sample
CVS		       js
program.properties.sample.~1.12.~
data		       jsp		  README
DCB_1035496690787.log  jspc_build	  README.~1.10.~
DCB_1054343490761.log  jspc_src		  TODO
DCB_1060903313342.log  jspc_srchome	  WEB-INF
doc		       jython
experimental	       lib
[dyoo at tesuque dyoo]$
###



Hope this helps!