为什么这个Python代码执行两次？

Question

I'm very new to Python and trying to learn how classes, methods, scopes, etc works by building very silly programs with no real purpose.

The code I wrote below is suppose to just define a class Functions that is instantiated using an x and a y value and then one can execute various simple math functions like add subtract, multiply or divide (yes I know there is a Python Math library).

However, whenever I run my code and I get to the section where I want to run a math function in my class it runs the entire program over again and then does the math function.

What am I doing wrong here?

The file name is MyMath.py

class Functions():

   def __init__(self, x, y):
       self.x = x
       self.y = y

   def add(self):
      return self.x+self.y

   def subtract(self):
       return self.x-self.y

   def multiply(self):
       return self.x*self.y

   def divide(self):
       return self.x/self.y

def check_input(input):
    if input == int:
        pass
    else:
        while not input.isdigit():
            input = raw_input("\n " + input + " is not a number.  Please try again: ")

    return input

print("Welcome to the customzied Math program!")
x = raw_input("\nTo begin, please enter your first number: ")
x = check_input(x)

y = raw_input("Enter your second number: ")
y = check_input(y)

from MyMath import Functions 

math = Functions(x,y)
print(math.add())

Answer 1

Remove the following statement.

from MyMath import Functions

The first line of the program defines the name Functions , and you can use it without having to import it. You only use the import command if the class (or function, or variable, ...) is defined in a different file/module.

Note in addition: When you import anything from a module the whole module is run as a script (although only the Functions name is imported into the local namespace). For this reason, everything within a file to be imported should be contained inside a class or function (unless there is a good reason not to...).