buggy python interpretter or am I missing something here?

[me]

I'm writing a linux daemon in python 2.x to process batches of GPS/GIS 
data and I'm running into something that seems to break the expected 
program flow in a REALLY BAD WAY.

Consider the attached template script and execute it with the -h option.  
It is falling through to the except: clause even though try to manually 
exit with sys.exit(0).  However, if I insert a "raise" into the except 
clause then the sys.exit(0) executes properly. 

See the attached code and output from when I run it.

Not interested in work-arounds.  I want to understand why it doesn't work 
as expected.

Thanks!

TCdaemon.py ----

#! /usr/bin/python

import sys


# 
------------------------------------------------------------------------------

defaultparams={ \
    "basedir": "/process", \
    "inpipe": "/tmp/TCdaemonIN", \
    "maxjobs":8, \
    "outpipe": "/tmp/TCdaemonOUT", \
    "ZZZ": 0
    }

# 
------------------------------------------------------------------------------

def parse_args(a,d):
    l=len(a)
    idx=1
    try:
        while (idx<l):
            if (a[idx]=="-#"):
                idx=idx+1
                d["maxjobs"]=int(a[idx])
            elif (a[idx]=="-d"):
                idx=idx+1
                d["basedir"]=a[idx]
            elif (a[idx]=="-h"):
                print "help goes here"
                sys.exit(0)
            elif (a[idx]=="-i"):
                idx=idx+1
                d["inpipe"]=a[idx]
            elif (a[idx]=="-o"):
                idx=idx+1
                d["outpipe"]=a[idx]
            idx=idx+1
    except:
        # raise # -- WTF!!!??? required for -h to not fall through to 
here?
        print "%s: error in command line - %s"%(a[0],a[idx:])
        sys.exit(1)

    
# 
------------------------------------------------------------------------------
# 
------------------------------------------------------------------------------
# 
------------------------------------------------------------------------------

if (__name__=="__main__"):
    print defaultparams
    parse_args(sys.argv,defaultparams)
    print defaultparams
    




output.txt ---
[@blackbox new]$ ./TCdaemon.py -h
{'ZZZ': 0, 'basedir': '/process', 'outpipe': '/tmp/TCdaemonOUT', 
'maxjobs': 8, 'inpipe': '/tmp/TCdaemonIN'}
help goes here
./TCdaemon.py: error in command line - ['-h']
[@blackbox new]$ echo $?
1
[@blackbox new]$ 
[@blackbox new]$ 
[@blackbox new]$ # editing to add "raise" at line 40
[@blackbox new]$ 
[@blackbox new]$ 
[@blackbox new]$ 
[@blackbox new]$ ./TCdaemon.py -h
{'ZZZ': 0, 'basedir': '/process', 'outpipe': '/tmp/TCdaemonOUT', 
'maxjobs': 8, 'inpipe': '/tmp/TCdaemonIN'}
help goes here
[@blackbox new]$ echo $?
0
[@blackbox new]$