Python3 function not returning complete list

Question

I'm trying to make a function that takes an input list parameter and do some math inside, returning a new list with the data collected from the math, but I'm always getting an empty list as a result. How do I need to pass the list to the function in order to get this to work?

inputArray = [12,6,7,3,8]

def derive (self, *inputArray):

    outputarray = []

    for i in inputArray:
        operatorA = inputArray[i]
        operatorB = inputArray[i+1]
        if operatorA > operatorB:
            operation = operatorA - operatorB
            outputarray.append(operation)
        else:
            operation = operatorB - operatorA
            outputarray.append(operation)
    print(outputarray)

 derive(inputArray)

You need to return the output value. Add `return outputarray` at the end of your function's body. — Right leg, Dec 20 '18 at 15:19
`for i in inputArray:` does not iterate indexes, but elements. Subsequent ` inputArray[i]` accesses seem misplaced. — user2390182, Dec 20 '18 at 15:21
And the `*inputArray` parameter seems to be wrong. Why the `*`? — Matthias, Dec 20 '18 at 15:23
"but I'm always getting an empty list as a result. " Not reproducible - the code causes an error instead, and has numerous problems. — Karl Knechtel, Aug 12 '22 at 04:51

score 1 · Accepted Answer · answered Dec 20 '18 at 15:27

You were misusing for. To iterate through index, you should use for i in range(len(inputArray) - 1). This will iterate through the list of indexes.

Also, you created a function that requires 2 arguments, but call it with just one, so I removed self.

And to finish, I believe you used the * in an attempt to refer to the string address. That's C/C++ syntax, but won't work on python. Instead, you can return the value to the original string:

inputArray = [12,6,7,3,8]

def derive (inputArray):

    outputarray = []

    for i in range(len(inputArray)-1):
        operatorA = inputArray[i]
        operatorB = inputArray[i+1]
        if operatorA > operatorB:
            operation = operatorA - operatorB

        else:
            operation = operatorB - operatorA

        outputarray.append(operation)
    print(outputarray)
    return(outputarray)

inputArray = derive(inputArray)

BTW, the whole function (without the printing) could be rewritten as: `def derive(values):` `return [abs(values[i] - values[i+1]) for i in range(len(values)-1)]`. — Matthias, Dec 21 '18 at 13:59
Alternative for the function body: `return [abs(i - j) for i, j in zip(values, values[1:])]` — Matthias, Dec 21 '18 at 14:02

Python3 function not returning complete list

1 Answers1