Passing a function as an argument inside another function

Question

def pivot2(arr,start=0,end=len(arr)):
    pivot=arr[start]
    swapid=start
    for x in range(start+1,end):
        if(pivot>arr[x]):
            swapid +=1
            swap(arr,swapid,x)
            print(arr)
    swap(arr,start,swapid)
    return swapid

def swap(arr,i,j):
    temp=arr[i]
    arr[i]=arr[j]
    arr[j]=temp

In pivot2 function I get an error that arr name not defined and when I remove end=len(arr) from the arguments the function works, why can't I pass len(arr) as an argument in Python?

Answer 1

because you are passing arr as an argument and it isn't a variable python will try find that variable raising that error

to fix this instead of putting len(arr) in the parameters put it inside the actual function

def pivot2(arr,start=0):
    end=len(arr)
    pivot=arr[start]
    swapid=start
    for x in range(start+1,end):
        if(pivot>arr[x]):
            swapid +=1
            swap(arr,swapid,x)
            print(arr)
    swap(arr,start,swapid)
    return swapid