Finding all local extrema from a list of values-CodePudding

This is my code, I receive an error that "list index out of range", I tried to solve this by accounting for the first and last value before the for loop, however I can not figure out how to make the for loop exclude the first and last object, any ideas?

def minmax(List):

    mins=[]
    maxs=[]

    if List[0]>List[1]: maxs.append(List[0])
    if List[0]<List[1]: mins.append(List[0])
        
    if List[-1]>List[-2]: maxs.append(List[-1])
    if List[0]<List[1]: mins.append(List[-1])
        
    for i in List[1:-1]:
        if List[i] < List[i-1] and List[i] < List[i 1]:
            mins.append(List[i])
        elif List[i] > List[i-1] and i> List[i 1]:
            maxs.append(List[i])
    return "mins",mins,"maxs",maxs
nums=[5,0,5,0,5]
minmax(nums)

CodePudding user response：

Your mistake lies in the way you access element in your for loop

for i in List[1:-1]:
        if List[i] < List[i-1] and List[i] < List[i 1]:
            mins.append(List[i])
        elif List[i] > List[i-1] and i> List[i 1]:
            maxs.append(List[i])

indeed, i here is an element of List not the index of this element, therefore, List[i] doesn't have any sense neither List[i 1] nor List[i-1].

One fix could be using enumerate to track either the current value of the list but also its index :

for n, i in enumerate(List[1:-1]):
        if List[n] < List[n-1] and List[n] < List[n 1]:
            mins.append(List[n])
        elif List[n] > List[n-1] and i> List[n 1]:
            maxs.append(List[n])

I strongly encourage you to use a debugger to understand this behavior.