[Tutor] returning values from function.

[Bala subramanian]

Friends,
I wrote the following code to create two different list. One containing data
points of all clusters and another containing list of individual cluster
data points. The script is as follows.

#!/usr/bin/env python
from sys import argv

# STEP 1: a) ACCUMULATING ALL DATA POINTS IN AND A LIST  b) CREATING LIST
OF  INDIVIDUAL CLUSTERS

print argv[1], argv[2]

data=[]  # list of all data points
all=[ [] for value in range(int(argv[2])) ]  # Creating an empty list of
lists of size n (No of clusters)

def cluster(infile=argv[1],n=int(argv[2])):
        for index, line in enumerate(infile):
            if line.startswith('#Consensus'):
                line=line.split()
                data.extend(line[2]) # data now should contain data points
of all clusters
        for value in range(n):
                for index, line in enumerate(data):
                    if data[index] == str(value):
                            zero=index+1
                            all[value].append(zero)
        #return data, all   ( I even tried by un commenting the return
statement )

print all
print data

The final print statement returns a empty list ie all and data. I have the
following queries

i) Why the print statement returns empty lists
ii) Is return really required here, if i understand the namespace well, the
function cluster actually modifies the global variables data and all.
iii) I even tried by using a return statement but still the script returns
empty list.
iv) Is there any fancy or better of way of doing this python.

Thanks,
Bala
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