Getting Index out of range error while trying to do Totaling statements

Question

I am trying to do a multiple totaling statements but it keeps saying index out of range. Here is the section of code:

for m in range(len(mo)):
  for o in range(len(mag)):
    if mag[o] == 0 and mo[m] ==1 :
        countfujita[m] = countfujita[m] + 1

and I am trying to get the totals into list a list such as this: countfujita = [0,0,0,0,0,0]

Answer 1

I suspect this is because you are looping over mag for every item in mo when this is not what you want. Let me know if the following fixes your issue:

for m in range(len(mo)):
  if mag[m] == 0 and mo[m] ==1 :
      countfujita[m] = countfujita[m] + 1

(this assumes that len(mag) = len(mo))

Answer 2

In order for your code to run successfully you need to ensure that countfujita is at least as long as the mo list.

The following would be a robust approach:

mo = [1, 0, 3]
mag = [3, 0, 1, 11]
# construct a list of the same length as *mo* and fill with zeroes
countfujita = [0] * len(mo)

for m in range(len(mo)):
    for o in range(len(mag)):
        if mag[o] == 0 and mo[m] == 1:
            countfujita[m] += 1

print(countfujita)

Output:

[1, 0, 0]

Answer 3

Indexing multiple lists inside nested loops is error-prone. In general we want to leverage the python built-in modules as much as possible.

For example (starting from the example defined by Lancelot du Lac) we can use itertools.product to generate all combinations of mo and mag. enumerate gives us the index corresponding to the element of mo:

from itertools import product

for (imo, xmo), xmag in product(enumerate(mo), mag):
    if (xmo, xmag) == (1, 0):
        countfujita[imo] += 1

---

To push this even further, we can combine this with Counter to first generate a list of all mo indices and then count. This results in a counter object Counter({0: 1}) object, similar to a dict, which might or might not be appropriate depending on what you do with countfujita later on:

from itertools import product
from collections import Counter

Counter([imo for (imo, xmo), xmag 
         in product(enumerate(mo), mag) 
         if (xmo, xmag) == (1, 0)])

# Counter({0: 1})