CODEWITHSUNDEEP
python
Cheetah jimi
Cheetah jimi

Reputation: 31

Got a solution but still get an indexError

I have written this python code. When I run it I get an index error at the end; I don't know why. I was wondering if someone could help me out.

The problem is to find the smallest positive number that is evenly divisible by all of the numbers from 1 to 20. My analysis is correct but just the code at the end is giving me hard time.

def leastCommonDenominator(num1, num2):
    '''
        Returns the least common denominator of two numbers
    '''
    num2List = range(1,num2+1)
    if num1 < num2:
        for i in num2List:
            if (num1*num2List[i]) % num2 == 0:
                return num1*num2List[i]
    num1List = range(1, num1+1)
    if num2 < num1:
        for i in num1List:
            if (num2*num1List[i]) % num1 == 0:
                return num2*num1List[i]
    else:
        return num1

def leastNum():
    '''
        Prints the least number divisible
    '''
    myList = range(1,4)
    print myList
    num = 1
    for i in myList:
        num = leastCommonDenominator(num, myList[i])
        print num    

def main():
    leastNum()

Upvotes: 1

Views: 90

Answers (2)

Tyranicangel
Tyranicangel

Reputation: 189

Use 

for i in myList:
    num = leastCommonDenominator(num,i)
    print num

instead of 

for i in myList:
    num = leastCommonDenominator(num,myList[i])
    print num

Here i is the iterator over the elements of the list.It is not over the index of elements.So you cannot use myList[i].On the other hand you can write

for i in range(0,len(myList)):
    num=leastCommonDenominator(num,myList[i])

Upvotes: 2

RocketDonkey
RocketDonkey

Reputation: 37259

When you define myList, its value is (as you know):

myList = [1, 2, 3]

When you iterate, you are cycling through each of the elements (1, 2, 3), but when you call leastCommonDenominator, you are using the index of the list, not the element itself (i.e. in the first pass through, you aren't calling the first element of myList, you are calling myList[1], which is the second element. This causes an IndexError on the final pass, because myList[3] is referring to the fourth element in the list, which as we can see does not exist (since range doesn't include the upper bound in its value). In order to fix, you should be able to do this:

num = leastCommonDenominator(num, i)

When you use the for loop like you are, you can simply use the values themselves. If you want to refer to the position of the elements, you can use enumerate, which returns both the index/position of a value and the value itself (this is more FYI - you don't need it here I don't believe :) ). For example:

for index, i in enumerate(myList):
    num = leastCommonDenominator(num, myList[index])

And you would get the same result.

Upvotes: 2

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