How to reference object variable from within method

Question

I'm still learning to work with objects. I defined vertices() as a method to return the vertices (initialized as vs) in Graph. I know that there is a more concise, elegant way to write vertices() but exactly how is escaping me.

Also specifically this relates to exercise 2.5 in Think Complexity: http://greenteapress.com/complexity/html/book003.html#toc12

class Graph(dict):
    def __init__(self, vs=[], es=[]):

        for v in vs:
            self.add_vertex(v)

    def add_vertex(self, v):
        """Add a vertex to the graph."""
        self[v] = {}

    def vertices(self):
        v = []
        for i in range(len(self)):
            v.append(i)
        return v

I think `add_vertex` and `vertices` methods should be indented. — mshsayem, May 17 '12 at 01:49
They should -- I wasn't pasting directly and that's my mistake. — Chris, May 17 '12 at 01:50
Also, don't use lists as default argument. http://stackoverflow.com/questions/1132941/least-astonishment-in-python-the-mutable-default-argument — mshsayem, May 17 '12 at 01:52
Shouldn't you actually be returning the keys of the dictionary, rather than a range of integers from 0 upwards? How exactly is the calling code supposed to use the result of `vertices`? — Karl Knechtel, May 17 '12 at 04:40

score 1 · Answer 1 · answered May 17 '12 at 01:58

1

You can make it one line with a list comprehension:

def vertices(self):
    return [i for i in range(len(self))]

answered May 17 '12 at 01:58

Odoood

11
1

1

Or just `return range(len(self))` for that matter. – Kirk Strauser May 17 '12 at 01:59
Haha yeah that too (as long as you're using python 2x) – Odoood May 17 '12 at 02:01
In 3.x, `list(range(len(self)))` suffices. – Karl Knechtel May 17 '12 at 04:39

score 1 · Answer 2 · answered May 17 '12 at 04:34

I defined vertices() as a method to return the vertices (initialized as vs) in Graph.

As vs in __init__ contains keys of the dict, i guess this is what you want.

    def vertices(self):
        return self.keys()

If so, you don't need vertices method at all - just always use Graph.keys()

How to reference object variable from within method

2 Answers2