Python: no more need for range(len(...))

I was practising my algorithm writing skills on CodeSignal and one of the problems is how to sum up a matrix where there are certain conditions placed on the columns and rows.

What's neat about CodeSignal is that you can view and up-vote or down-vote other people's solutions after you have submitted your solution. Even in small algorithm problems, you can see how others are making use of clever tricks and libraries within the programming language used.

For instance, I used the Python enumerate function to traverse the rows and columns of the matrix:

for i, row in enumerate(matrix):
    for j, col in enumerate(row):
        print('matrix[{}][{}] = {}'.format(i, j, col))

I noticed that other solutions to the problem were using this pattern:

for i in range(len(matrix)):
    for j in range(len(matrix[i])):
        print('matrix[{}][{}] = {}'.format(i, j, matrix[i][j]))

This is something that makes sense in languages like C, C++ or JavaScript or even in Java. However, if there are iterators available that give you both the index and value, you should use them and match the idioms of the language.

Although, you do have to remember that when iterating over a slice of an array, you will need to set the starting index that enumerate starts at:

string = 'awesome'
for i, c in enumerate(string):
    print(i, c) # prints 0, a to 6, e
for i, c in enumerate(string[1:]):
    print(i, c) # prints 0, w to 5, e
for i, c in enumerate(string[1:], 1):
    print(i, c) # prints 1, w to 6, e

On the flip side, I found a solution that was clever and used a combination of Python's itertools takewhile function, and the built-in sum and map functions.

There's a lot that all developers can learn, even in the smallest problems.