Question

I have the following code, where I use a class stat to keep my data. Objects of type stat are inserted in a list. However, when I try to call the method printStats, I get the error, AttributeError: stat instance has no attribute 'printStats'. Secondly I want to know how can I sort the list containing objects of stat. My sorting should be based on the blocks field of stat.

fi = open( 'txt/stats.txt', 'r' )
fo = open( 'compile/stats.txt', 'w' )
list = []

class stat():
    def __init__(self, fname, blocks, backEdges):
        self.fname = fname
        self.blocks = blocks
        self.backEdges = backEdges
    def printStats(self):
        print self.fname + str(self.blocks) + str(self.backEdges)

while True:
    line_str = fi.readline()
    if line_str == '':
        break

    str = line_str.split()
    list.append( stat(str[0], int(str[1]), int(str[2])) )

for item in list:
    item.printStats() # <-- problem calling this

Answer 1

As far as the sorting is concerned, you definitely can use the key function:

import operator
lst.sort(key=lambda x: x.blocks)
lst.sort(key=operator.attrgetter('blocks') ) #alternative without lambda.

However, if you want to be able to compare stats objects in a non-sorting context, you can override __eq__,__gt__,__lt__ (and to make your life easier, you can use the functools.total_ordering class decorator to define most of the comparisons for you):

import functools
@functools.total_ordering
class stats(object): #inherit from object.  It's a good idea
    def __init__(self, fname, blocks, backEdges):
        self.fname = fname
        self.blocks = blocks
        self.backEdges = backEdges
    def printStats(self):
        print self.fname + str(self.blocks) + str(self.backEdges)
    def __eq__(self,other):
         return self.blocks == other.blocks
    def __lt__(self,other):
         return self.blocks < other.blocks

with stats defined this way, sorting should again be as simple as:

lst.sort()  #or if you want a new list:  new_lst = sorted(lst)