pythonmultidimensional-array

How to initialize a two-dimensional array (list of lists, if not using NumPy) in Python?


I'm beginning python and I'm trying to use a two-dimensional list, that I initially fill up with the same variable in every place. I came up with this:

def initialize_twodlist(foo):
    twod_list = []
    new = []
    for i in range (0, 10):
        for j in range (0, 10):
            new.append(foo)
        twod_list.append(new)
        new = []

It gives the desired result, but feels like a workaround. Is there an easier/shorter/more elegant way to do this?


Solution

  • A pattern that often came up in Python was

    bar = []
    for item in some_iterable:
        bar.append(SOME EXPRESSION)
    

    which helped motivate the introduction of list comprehensions, which convert that snippet to

    bar = [SOME_EXPRESSION for item in some_iterable]
    

    which is shorter and sometimes clearer. Usually, you get in the habit of recognizing these and often replacing loops with comprehensions.

    Your code follows this pattern twice

    twod_list = []                                       \                      
    for i in range (0, 10):                               \
        new = []                  \ can be replaced        } this too
        for j in range (0, 10):    } with a list          /
            new.append(foo)       / comprehension        /
        twod_list.append(new)                           /