CODEWITHSUNDEEP
python-3.x
Karl LeTourneau
Karl LeTourneau

Reputation: 37

Index Error: list index out of range (Python beginner, while loops)

I am trying to make a function that takes in a list as an input parameter. I am to use a while loop to iterate over the list and keep track of the amount of integers and strings that are included in the list. This is what i have so far:

def usingwhileloop(mylist):
    count = 0
    int_total = 0
    str_total = 0

    while count <= len(mylist):
        if isinstance(mylist[count], int) == True:
            int_total = int_total + 1

        elif isinstance((mylist[count]), str) == True:
            str_total = str_total + 1


        count = count + 1

    newlist = [int_total, str_total]
    return newlist

When I run for a list like [1, 2, 3, “a”, “b”, 4] it should return [4, 2] but instead i get the following error: "line 51, in usingwhileloop if isinstance(what[count], int) == True: IndexError: list index out of range"

what am i doing wrong? I struggle with while loops...

Upvotes: 2

Views: 63

Answers (2)

cEz
cEz

Reputation: 5062

If you really require a while loop then see the answer by josephting.

For the example that you have shown though, you don't need a while loop, e.g.

"""
Some simple functions
"""
def count_types_ex1(items):
    """Count types from a list"""
    counters = [0, 0]
    for item in items:
        if isinstance(item, int):
            counters[0] += 1
        elif isinstance(item, str):
            counters[1] += 1
    return counters

print(count_types_ex1([1, 2, 3, 'a', 'b', 4]))

def count_types_ex2(items):
    """Count types from a list"""
    check_type = lambda x: [int(isinstance(x, int)), int(isinstance(x, str))]
    counters = [check_type(x) for x in items]
    return sum(x[0] for x in counters), sum(x[1] for x in counters)

print(count_types_ex2([1, 2, 3, 'a', 'b', 4]))

Output:

[4, 2]
(4, 2)

Upvotes: 1

josephting
josephting

Reputation: 2665

It's because you were trying to access an item from the list that doesn't exist.

Why? Assuming we're using this list as example - [1, 2, 3, “a”, “b”, 4]

count starts from 0 so I assume you expect count to go from 0 to 5.

0: 1
1: 2
2: 3
3: "a"
4: "b"
5: 4

However, len(mylist) is 6 so the loop will attempt to access mylist[6] which does not exist.

You have to modify your while loop to stop at 5 instead. To do that, while count <= len(mylist) - 1: or while count < len(mylist): will do.

Upvotes: 1

Related Questions