Class and Array Problems

Question

I am absolutely useless with python and I'm struggling to do what seems to be simple things. I need to read a text file which contains a network routing table which contains the distance between each node on the network (below)

0,2,4,1,6,0,0
2,0,0,0,5,0,0
4,0,0,0,0,5,0
1,0,0,0,1,1,0
6,5,0,1,0,5,5
0,0,5,1,5,0,0
0,0,0,0,5,0,0

I then need to assign it to a two dimensional array which I have done with the code i have written below..

Network = []
NodeTable = []
def readNetwork():
    myFile = open('network.txt','r')
    for line in myFile.readlines():
        line.strip(' \n' '\r') 
        line = line.split(',')
        line = [int(num) for num in line]
        Network.append(line)

Once that has been done I then need to iterate through the Network array and add each horizontal line to another array which will hold information about the nodes, but as far as I have been able to get with that is here:

class Node(object):
     index = #Needs to start from A and increase with each node
     previousNode = invalid_node
     distFromSource = infinity
     visited = False


NodeTable.append(Node())

So that array will be initialised as:

A  invalid_node  infinity  False
B  invalid_node  infinity  False
C  invalid_node  infinity  False
...
etc

Could anyone give me a hand with creating each node in the NodeTable array?

Answer 1

Redundant line

Strings in Python are immutable, thus with the following line:

line.strip(' \n' '\r') 

you are only getting a copy of the line string, stripped of some characters, but you do not assign it to anything. Change it into:

line = line.strip(' \n' '\r') 

As DSM pointed out in the comments, it will not change much, as int will just ignore redundant whitespaces.

Mapping string to ints

You also are mapping strings to ints like that:

line = [int(num) for num in line]

which could be replaced by clearer:

line = map(int, line)

and should give you some slight performance gain also. To shorten your code, you can also replace the following lines:

line.strip(' \n' '\r') 
line = line.split(',')
line = [int(num) for num in line]
Network.append(line)

with the following:

Network.append(map(int, line.split(',')))

How to increase Node's index attribute with each instance

This could be done like that:

>>> class Node(object):
    baseindex = '@'  # sign before "A"
    def __init__(self):
        cls = self.__class__
        cls.baseindex = chr(ord(cls.baseindex) + 1)
        self.index = self.baseindex
        self.previousNode = 'invalid_node'
        self.distFromSource = 'infinity'
        self.visited = False


>>> a = Node()
>>> a.index
'A'
>>> b = Node()
>>> b.index
'B'
>>> a.index
'A'

As you can see baseindex is attached to the class, and index is attached to the class's instance. I suggest you should attach every instance-specific variable to the instance, as shown in the example above.

Adding Node into the list as list

One of the easiest ways to insert it as list into another list, is to add a method returning it as list (see as_list() method):

>>> class Node(object):
    baseindex = '@'  # sign before "A"
    def __init__(self):
        cls = self.__class__
        cls.baseindex = chr(ord(cls.baseindex) + 1)
        self.index = self.baseindex
        self.previousNode = 'invalid_node'
        self.distFromSource = 'infinity'
        self.visited = False
    def as_list(self):
        return [self.index, self.previousNode, self.distFromSource,
            self.visited]


>>> a = Node()
>>> a.index
'A'
>>> a.as_list()
['A', 'invalid_node', 'infinity', False]

so you should be able to add nodes like this:

NodeTable.append(Node().as_list())

But remember - after doing the above, you will not get list of Node instances, you will get list of lists.