[Python-Dev] first correct explanation wins a beer...

26 Feb 2001

      ...or the caffeinated beverage of your choice, collectable
at IPC9.

I'm running on a straightforward Linux box:

$ uname -a
Linux akbar.nevex.com 2.2.16 #3 Mon Aug 14 14:43:46 EDT 2000 i686 unknown

with Python 2.1, built fresh from today's repo:

$ python
Python 2.1a2 (#2, Feb 26 2001, 15:27:11)
[GCC egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)] on linux2

I have one tiny script called "tryout.py":

$ cat tryout.py
print "We made it!"

and a small HTML file called "printing.html":

$ cat printing.html
<html><body>

</body></html>

The idea is that my little SAX handler will look for "pre" elements
with "prog" attributes, re-run the appropriate script, and compare
the output with what's in the HTML page (it's an example for the
class).

The problem is that "popen2" doesn't work as expected when called
from within a SAX content handler, even though it works just fine
when called from a method of another class, or on its own.  The
whole script is:

$ cat repy
#!/usr/bin/env python

import sys
from os import popen2
from xml.sax import parse, ContentHandler

class JustAClass:

    def method(self, progName):
        shellCmd = "python " + progName
        print "using just a class, shell command is '" + shellCmd + "'"
        inp, outp = popen2(shellCmd)
        inp.close()
        print "using just a class, result is", outp.readlines()

class UsingSax(ContentHandler):

    def startElement(self, name, attrs):
        if name == "pre":
            shellCmd = "python " + attrs["prog"]
            print "using SAX, shell command is '" + shellCmd + "'"
            inp, outp = popen2(shellCmd)
            inp.close()
            print "using SAX, result is", outp.readlines()

if __name__ == "__main__":

    # Run it directly
    inp, outp = popen2("python tryout.py")
    inp.close()
    print "Running popen2 directly, result is", outp.readlines()

    # Use a plain old class
    JustAClass().method("tryout.py")

    # Using SAX
    input = open("printing.html", 'r')
    parse(input, UsingSax())
    input.close()

The output is:

$ python repy
Running popen2 directly, result is ['We made it!\n']
using just a class, shell command is 'python tryout.py'
using just a class, result is ['We made it!\n']
using SAX, shell command is 'python tryout.py'
using SAX, result is []

My system has a stock 1.5.2 in /usr/bin/python, but my path is:

$ echo $PATH
/home/gvwilson/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/usr/sbin:/ho
me/gnats/bin

so that I get the 2.1 version:

$ which python
/home/gvwilson/bin/python

My PYTHONPATH is set up properly as well (I think):

$ echo $PYTHONPATH
/home/gvwilson/lib/python2.1:/home/gvwilson/lib/python2.1/lib-dynload

I'm using PyXML-0.6.4, built fresh from the .tar.gz source today.

So, like I said --- a beer or coffee to the first person who can
explain what's up.  I'm attaching the Python scripts, the HTML
file, and a verbose strace output from my machine.

Thanks,
Greg

 <<printing.html>>  <<repy>>  <<strace.txt>>  <<tryout.py>>

[Python-Dev] first correct explanation wins a beer...

Greg Wilson