2D array of objects in Python

Question

I'm converting some java code to python code and I ended up getting stumped on how to convert a 2D array of objects in Java to python.

Java code:

private Node nodes[][] = new Node[rows][columns];

How would I do this in python?

Basically, a list of lists. But it's very likely that there's no reason to start with initializing the list. See if a list comprehension works in your case, else write it as a loop with nodes.append([]) and nodes.extend or nodes.append in another loop. — user395760
– user395760, Commented Jun 25, 2011 at 20:55

JBernardo · Accepted Answer · 2011-06-25 21:17:32Z

13

I think that's what you want

nodes = [[Node() for j in range(cols)] for i in range(rows)]

But it is not always a good practice to initialize lists. For matrices it may make sense.

If you're wondering: Documentation about list comprehensions

Demo code:

>>> class Node:
      def __repr__(self):
        return "Node: %s" % id(self)
>>> cols = 3
>>> rows = 4
>>> nodes = [[Node() for j in range(cols)] for i in range(rows)]
>>> from pprint import pprint
>>> pprint(nodes)
[[Node: 41596976, Node: 41597048, Node: 41596904],
 [Node: 41597120, Node: 41597192, Node: 41597336],
 [Node: 41597552, Node: 41597624, Node: 41597696],
 [Node: 41597768, Node: 41597840, Node: 41597912]]

edited Jun 25, 2011 at 21:17

answered Jun 25, 2011 at 20:55

JBernardo

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4 Comments

nobody Over a year ago

curious if you forgot a [ ] in there?

nobody Over a year ago

It looks funny; I would have assumed it would have been something like: nodes = [[Node() for j in range(cols)], [for i in range(rows)]]

JBernardo Over a year ago

@nobody what you wrote doesn't even work. I used nested list comprehensions

ArtOfWarfare Over a year ago

Couldn't/shouldn't you use _ in place of the names j and i, given that you're only including anything there for synthetic reasons and you don't actually want the values stored anywhere?

user625768 · Accepted Answer · 2013-02-16 12:19:23Z

0

Python doesnt really do 2d arrays. Here is a better explenation

Its does lists instead

answered Feb 16, 2013 at 12:19

user625768

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