2D arrays in Python

>>> a = []>>> for i in xrange(3):...     a.append([])...     for j in xrange(3):...             a[i].append(i+j)...>>> a[[0, 1, 2], [1, 2, 3], [2, 3, 4]]>>>

Depending what you're doing, you may not really have a 2-D array.

80% of the time you have simple list of "row-like objects", which might be proper sequences.

myArray = [ ('pi',3.14159,'r',2), ('e',2.71828,'theta',.5) ]myArray[0][1] == 3.14159myArray[1][1] == 2.71828

More often, they're instances of a class or a dictionary or a set or something more interesting that you didn't have in your previous languages.

myArray = [ {'pi':3.1415925,'r':2}, {'e':2.71828,'theta':.5} ]

20% of the time you have a dictionary, keyed by a pair

myArray = { (2009,'aug'):(some,tuple,of,values), (2009,'sep'):(some,other,tuple) }

Rarely, will you actually need a matrix.

You have a large, large number of collection classes in Python. Odds are good that you have something more interesting than a matrix.

In Python one would usually use lists for this purpose. Lists can be nested arbitrarily, thus allowing the creation of a 2D array. Not every sublist needs to be the same size, so that solves your other problem. Have a look at the examples I linked to.