variable referenced before assignment

[Niko047]

Thanks guys, as you advised I assigned the variable inside that second function and I put a while loop after that, and it worked.

def main():
    number = int(input("Insert the number:"))
    if number == "":
        print("Goodbye!")
    elif number < 0:
        print("Error: negative number")
    else:
        def estim(someNumber):
            estimation = 1
            while True:
                estimation = (estimation + someNumber / estimation) / 2
                tollerance = 0.000000001
                difference = abs(number - estimation **2)
                if difference <= tollerance:
                    break
            return estimation
    return estim(number)