Python UnboundLocalError on my function return. Something to do with try except?

Question

def analyzeList(lst):
    try:
        #minimum
        min = 0
        currentmin = float(lst[0])
        for i in range(0, len(lst)-1):
            if currentmin > float(lst[i+1]):
                currentmin = float(lst[i+1])
                min = currentmin
        print(min)
        #maximum
        max = 0
        currentmax = float(lst[0])
        for i in range(0, len(lst)-1):
            if currentmax < float(lst[i+1]):
                currentmax = float(lst[i+1])
                max = currentmax
        print(max)
        #sum
        sum = 0
        for i in lst:
            sum += i
        
        average = (sum/len(lst))
    
    except ValueError:
        pass
    
    return min, max, sum, average

This is my code. I’m trying to get min, max, sum, and average of list that has random number and letters.
Been trying for hours, not sure how to get the pass UnboundLocalError min referenced before assignment.

I tried putting the return inside the try except but that did returned nothing which is as expected but it didn’t give me any error code. Seems like the return is thinking that there is no min, max variable?

Error:

Exception has occurred: UnboundLocalError
local variable 'max' referenced before assignment
  File "C:UsersdavidDesktopPractice Python Filesquestions.py", line 60, in analyzeList
    return min, max, sum, average

  File "C:UsersdavidDesktopPractice Python Filesquestions.py", line 70, in main
    data = analyzeList(numbers)

  File "C:UsersdavidDesktopPractice Python Filesquestions.py", line 73, in <module>
    main()
UnboundLocalError: local variable 'max' referenced before assignment

Asked By: Pixalte

||

Source

Answer 1

The problem happens when the code hits the first thing in lst that can’t be converted to a float. A ValueError is raised while calculating min and your code never gets to assigning an initial value to max. Execution drops out of the exception handler and you try to return a max that never had any value bound to it.

I’m going out on a limb here, but it seems like you want to get stats on the subset of the list that can be converted to a float. That means you need your exception handling inside of the loop. Its easiest to get the float conversion done early and deal with that list for sums and etc.

Python has functions for min, max and sum, so no need to do this manually …. but I did anyway.

def analyzeList(lst):
    floaters = []
    for value in lst:
        try:
            floaters.append(float(value))
        except ValueError:
            pass

    if not floaters:
        return ??? no floats, what should this be?
        
    min = max = sum = floaters[0]
    for value in floaters[1:]:
        if min > value:
            min = value
        if max < value:
            max = value
        sum += value
    average = sum/len(floaters)
    return min, max, sum, average

You could slim this down with

def analyzeList(lst):
    floaters = []
    for value in lst:
        try:
            floaters.append(float(value))
        except ValueError:
            pass

    if not floaters:
        return ??? no floats, what should this be?
  
    return min(floaters), max(floaters), mysum:=sum(floaters), mysum/len(floaters)

Answered By: tdelaney

Python UnboundLocalError on my function return. Something to do with try except?

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