[Tutor] Re: Using a dictionary to keep a count

[Levy Lazarre]

On Sat, 02 Aug 2003 21:07:41 +0200,   sigurd@12move.de  wrote:  

>(c) So a function to process log files and print the values could be
>    written like that: 

>def process_log_file(name):
>    d = {}
>    f = open(name)
>    for line in f:
>        script, address = process_line(line)
>        d[address] = d.setdefault(address,0) + 1
>    f.close()
>    for (key, value) in d.items():
>        print key, " => ", value

Thanks for the clarification and suggestion, however this approach doesn't
work for it doesn't create the intended dictionary of dictionaries
structure.
What I needed was the count per script per site, something like:
dic =  {
       '/cgi-bin/script1.cgi' => {
                                       'alpha.umn.edu' => 2,
                                       'rohcs.ats.com' => 2
                                        },
      '/cgi-bin/script2.cgi' => {
                                       'rohcs.ats.com' => 1,
                                       'idg.com' => 1
                                       }
 }

The following approach using exceptions seems to work:
###############################################
dic ={} 

# Read the file line by line and extract the script name and the address.
f = file('access_log')
for line in f :
    script, address = process_line(line)   
    try:             
      dic[script]                       # Has this script already been seen?
    except KeyError:     
      dic[script] = {}                  # first time script is seen, set
empty dict for it 
      
    try:      
      dic[script][address] += 1         # Has this address already been seen
for this script?
                                                  # if so, increment its
count
    except KeyError:    
       dic[script][address] = 1         # first time address seen for this
script, count = 1
f.close()
# Now print the dictionary to verify what we have done:

for key in dic.keys():
    print key, " => "
    for value in dic[key].keys():
        print value+":", dic[key][value]
     
    print "\n"    
#############################################################
Any comments? Is this a bad style? I was trying to make the code shorter
with setdefault(), but it appears very difficult to use with nested
structures.

Thanks,
Levy Lazarre
llazarre@yahoo.com


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