خطا عجیب در پایتون

سلام من در حال یادگیری پایتون هستم
یه کد توی vs code نوشتم و ماشین حساب درست کردم و الان دارم ارور هاش رو تنظیم میکنم و فکر میکنم آخرای کارم
اینم کد:

import os

def calc(a):
    num1 = ""
    num2 = ""
    turn = 1
    operation = ""
    for select in str(a):
        if(select in "0123456789 "):
            if(turn == 1):
                num1 += select
            else:
                num2 += select
        elif(select in "+-*/%<>"):
            if(num1 == ""):
                print("invalid")
                global Error
                Error = True
                break
            else:
                turn = 2
                operation += select
        else:
            print("invalid")
            break
    if(Error):
        Error = False
    elif(num2 == ""):
        print("invalid")
    else:
        if(operation == "+"):
            print(int(num1) + int(num2))
        elif(operation == "-"):
            print(int(num1) - int(num2))
        elif(operation == "*"):
            print(int(num1) * int(num2))
        elif(operation == "/"):
            print(int(num1) / int(num2))
        elif(operation == "**"):
            print(int(num1) ** int(num2))
        elif(operation == "%"):
            print(int(num1) % int(num2))
        elif(operation == "<"):
            if(int(num1) < int(num2)):
                print("Yes")
            else:
                print("No")
        elif(operation == ">"):    
            if(int(num1) > int(num2)):
                print("Yes")
            else:
                print("No")
        else:
            print("invalid")

os.system("cls")

print("\nWelcome To Calculator!\nEnter 'Z' To Exit\nEnter 'C' To Clear")
print(20 * "--" + "\n")

while True:
    Entrance = input()
    if(Entrance in "zZ"):
        print("Okay")
        break
    if(Entrance in "cC"):
        os.system("cls")
        print("\nWelcome To Calculator!\nEnter 'Z' To Exit\nEnter 'C' To Clear")
        print(20 * "--" + "\n")
        continue
    calc(Entrance)

فقط یه مشکل دارم اونم اینه که من اینجا متغیر Error رو تنظیم کردم ولی....

def calc(a):
    num1 = ""
    num2 = ""
    turn = 1
    operation = ""
    for select in str(a):
        if(select in "0123456789 "):
            if(turn == 1):
                num1 += select
            else:
                num2 += select
        elif(select in "+-*/%<>"):
            if(num1 == ""):
                print("invalid")
                global Error
                Error = True
                break
            else:
                turn = 2
                operation += select
        else:
            print("invalid")
            break

وقتی میخوام توی if ازش استفاده کنم میزنه تعریف نشده
اینجا گذاشتم ببینید مشکلی داره؟

if(Error):
    Error = False

اینم ارورش

File "c:\Users\CaratechCO\Desktop\code\py2\Calculator.py", line 71, in <module>
    calc(Entrance)
  File "c:\Users\CaratechCO\Desktop\code\py2\Calculator.py", line 26, in calc
    if(Error):
       ^^^^^
NameError: name 'Error' is not defined. Did you mean: 'OSError'?
PS C:\Users\CaratechCO\Desktop\code\py2>