Python 3: List inside dictionary, list index out of range

Question

I have created a dictionary where the entries are lists like this:

new_dict
{0: ['p1', 'R', 'p2', 'S'], 1: ['p3', 'R', 'p4', 'P'], 2: ['p5', 'R', 'p6', 'S'], 3:   ['p7', 'R', 'p8', 'R'], 4: ['p9', 'P', 'p10', 'S'], 5: ['p11', 'R', 'p12', 'S'], 6: ['p13', 'S', 'p14', 'S']}

From here I am trying to check that the elements inside the lists are in my list below Moves. For example, in new_dict[0], I want to check that the 1st element and the third element in Moves, if not, raise the class exception. (This is a snippet of the code.)

class NoStrategyError(Exception): pass

j=0
while j < len(new_dict):
    i = 0
    while i < 4:
        # Write the code for the NoSuchStratgyError 
        Moves = ['R', 'S', 'P', 'r', 's', 'p']
        if new_dict[j][1+4*i] not in Moves or new_dict[j][3+4*i] not in Moves:
            raise NoStrategyError("No such strategy exists!")
        i+=1
    j+=1

Now here is the problem, when I run this, I get the following error:

if new_dict[j][1+4*i] not in Moves or new_dict[j][3+4*i] not in Moves: IndexError: list index out of range

What does this mean?

Is there a better way to write the inner while loop? And change it instead to a for loop? Something like, for elem in new_dict[j]?

Your lists have a maximum of 4 elements, but `1 + 4 * i` goes from 1 to 13. — Blender, Jun 28 '13 at 23:55
I just realized it. I don't need that inner `while loop`. Phew! — Student J, Jun 29 '13 at 00:04
Also, why are you using a dictionary with consecutive integer keys instead of a list? — Blender, Jun 29 '13 at 00:05
The keys represent the n-th game played. But really, it was also because I had to regroup a flattened list by fours. I didn't know how to do that without using a dictionary. — Student J, Jun 29 '13 at 00:43
May be helpful: http://stackoverflow.com/questions/312443/how-do-you-split-a-list-into-evenly-sized-chunks-in-python — Blender, Jun 29 '13 at 00:45

blehman · Accepted Answer · 2013-06-29T07:19:23.340

Notice that in the first interation of your nested loop, we see the following values that are both in Moves:

>>>new_dict[0][1], new_dict[0][3] 
('R', 'S')

However, on your second iteration in the nested loop, you are trying to evaluate terms that are not included in the dictionary:

>>>new_dict[1][5], new_dict[1][7]
IndexError: list index out of range

Notice that new_dict[1] only has 4 elements:

>>>new_dict[1]
['p3', 'R', 'p4', 'P']

So you can only reference new_dict[1][0],new_dict[1][1],new_dict[1][2],new_dict[1][3]:

>>>new_dict[1][0],new_dict[1][1],new_dict[1][2],new_dict[1][3]
('p3', 'R', 'p4', 'P')

Python 3: List inside dictionary, list index out of range

1 Answers1