Solving error: "list index out of range" in Python

Question

The code is giving the correct answer for all test cases except when I enter a list such as [1,2,3,4,5]. Then it shows:

IndexError: list index out of range.

Why is this happening? Shouldn't the else statement at the end take care of this?

def func(n):
    my_list = n.split()
    l = []

    for i in my_list:
         l.append(int(i))

    if len(l)==0 or len(l)==1:
        return None

    for k in range(0, len(l)):
        if l[k+1] >= l[k] + 2:
            return l[k+1]
        else:
            return None

n = input()

print(func(n))

The k+1 in l[k+1] in the if condition is out of range anyway — ForceBru
– ForceBru, Commented May 15, 2020 at 19:28
With for k in range(0,len(l)), k will go from 0 to len(l)-1. This causes l[k+1] to get out of range in if l[k+1]>=l[k]+2: when k equals len(l)-1. — DarrylG
– DarrylG, Commented May 15, 2020 at 19:29
Can you specify the exact input you're typing in? Because I can't reproduce your error, nor do I expect to be able to. You'll never iterate off the end of the list because you always return after either of the branches in the if/else. That's probably not really what you want, but you shouldn't be getting an IndexError. Please make sure this is a minimal reproducible example. If it's not reproducible with your code, it doesn't do us much good! — Blckknght
– Blckknght, Commented May 16, 2020 at 1:47

Mario Ishac · Accepted Answer · 2020-05-15 19:29:01Z

4

The error appears here:

for k in range(0,len(l)):
    if l[k+1]>=l[k]+2:
        return l[k+1]
    else:
        return None

Because you iterate up to k = len(l) - 1 inclusively, k + 1 on the last iteration will be len(l), which is out of bounds. Instead, you should change the for to:

for k in range(0, len(l) - 1):
    ...

Now, the value of k + 1 on the last iteration will be len(l) - 2 + 1 = len(l) - 1, which is within the bounds of l.

answered May 15, 2020 at 19:29

Mario Ishac

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1 Comment

Blckknght Over a year ago

While what you describe is an error in the code, it can't actually happen in the version of the code written in the question because it always returns on the first iteration.

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