Variable issues in if statements

I've just started python and I've decided to start with a simple program to parse a single line, two argument mathematical expression directly into an answer. Examples: 4 + 2, 3/4, 5435 * 3423, ect. To start with I'm trying to interpret the two variables in the equation before I work on having the program mathify them. My problem is the lines 39, 40, 42, and 43 are not modifying their respective variables at 1, 3, 2, and 5. In PyCharm, they are greyed out with an error about shadowing names out of scope.

It is currently almost 1AM and I'm not much of a night owl (I'll never make it as a coder lol) so it's probably a stupid mistake on my part but just in case...

primeNumber = None
secNumber = None
num11 = 0
buildList = []
finished = False

def interpret(statement):
    i = 0
    iMax = len(statement)
    while True:
        if i >= iMax:
            break
        parse(statement[i])
        i = i + 1

def parse(char, buildList=buildList):
    interrupt = [" ", "+", "-", "/", "*"]
    if char in interrupt:
        buildNumber(buildList)
        buildList.clear()
    elif num11 == 1:
        buildNumber(buildList)
        buildList.clear()
    else:
        buildList.append(char)

def isNumber(att):
    try:
        int(att)
        return True
    except ValueError:
        return False

def buildNumber(finishedList, num11 = num11):
    finishedNumber = ''.join(finishedList)
    print(finishedNumber)

    if num11 == 0:
        primeNumber = finishedNumber # <<< line 39
        num11 = 1
    elif num11 == 1:
        secNumber = finishedNumber
        finished = True