我的“非常简单”的Python计算器出现问题

Question

I have written another simple program that I call my basic 'Python Calculator.' So far, I have found a problem with some of the code that I have written in Python 3.3.2. Here is the code below so you can read it before I state my problem...

def startup_screen():
    user_input_1 = int(input("Please enter your first number.\n"))
    user_input_2 = int(input("Now please enter your second number.\n"))
    command_list()

def command_list():
    user_command = input("Now what would you like to do with these two numbers?\n").lower()

    if user_command == "add":
        calc_add()
    elif user_command == "subtract":
        calc_subtract()
    elif user_command == "multiply":
        calc_multiply()
    elif user_command == "divide":
        calc_divide
    else:
        print("Please try again.")
        user_command

def calc_add():
    add_result = (user_input_1+user_input_2)
    print(add_result)
    command_list()

def calc_subtract():
    subtract_result = (user_input_1-user_input_2)
    print(subtract_result)
    command_list()

def calc_multiply():
    multiply_result = (user_input_1*user_input_2)
    print(multiply_result)
    command_list()

def calc_divide():
    divide_result = (user_input_1/user_input_2)
    print(divide_result)
    command_list()

startup_screen()

Here, you can see that I have defined the startup_screen , which collects user input as an integer and then stores it respectively in user_1 and user_2 . Then, the user is taken to the command home screen where they can choose to either add, subtract, multiply or divide both numbers. The command is then determined from the user input, so if the user wants to add two numbers, they type in 'add' and they are taken to the add function - as defined above.

However , in the add function, the user_1 and user_2 inputs are not recognized, as well as in the other programs... so it causes an error in the in the program. I have no idea what to do. Could you please help me?

Thank you very much...

Answer 1

Give the inputs as arguments to the functions that follow, the values are not global variables (not immediately accessible by any function) if they are defined within a function.

def loadscreen():
    ...
    command_home(user_input_1,user_input_2)

def command_home(user_input_1,user_input_2):
    ...
    calc_add(user_input_1,user_input_2)

def calc_add(user_input_1,user_input_2)
    add_result = (user_input_1 + user_input_2)
    print(add_result)

Answer 2

Lets look at you program from the point of view of the def calc_add(): function.

In the first line,

add_result = (user_input_1 + user_input_2)

you say, take the value of user_input_1 add it to user_input_2 and make that into the variable add_result . Okay that makes sense.

Now lets get the first value user_input_1 ... lets see, first place to check is the 'local scope'. That is the function i am currently in.

def calc_add():
    add_result = (user_input_1 + user_input_2)
    print(add_result)

Okay nope, nothing there... okay maybe it was one of the input parameters ?

def calc_add():

Nope no input parameters were passed to this function. Okay it must be global ... but wait crap... no global parameters are ever decalred! especially not user_input_1 . Well dang it, im supposed to add two parameters but one of the parameters doesnt exist! Thats not possible I better throw an error!

Maybe if the programmer had passed me the information i needed it would work better, Maybe something like this :

def load_screen():
    user_1 = int(input("Please enter your first number.\n"))
    user_2 = int(input("Now please enter your second number.\n"))
    command_home( user_1, user_2) # Okay command_home I took 2 inputs! 
                                  # Here they are work your magic!



def command_home(in1, in2): # Hey I need 2 varaibles to work, Ill call them in1 and in2.
                            # so based on the way command_home( user_1, user_2) is called
                            # in1 = user_1, in2 = user_2 
    command = input("Now what would you like to do with these two numbers?\n").lower()
    if command == "add":
        calc_add(in1, in2) #Okay, now i need to add my two inputs,
                           # but calc_add is another function it wont be able to see MY
                           # in1, in2 ...  i better pass them over as parameters.
    elif command == "subtract":
        calc_subtract()
    elif command == "multiply":
        calc_multiply()
    elif command == "divide":
        calc_divide()



def calc_add(user_input_1,user_input_2 ): # Okay now i know where to look for user_input_1 
                                          # and user_input_2, they will be passed to me
                                          # when someone calls me! Now i can find my varables
                                          # and i wont throw an error!
    add_result = (user_input_1 + user_input_2)
    print(add_result)

Answer 3

You are not passing the user's input into the later functions which rely on it, such as calc_add().

The way to fix this problems would be to modify your code like so:

def startup_screen():
    user_1 = int(input("Please enter your first number.\n"))
    user_2 = int(input("Now please enter your second number.\n"))
    command_home(user_1,user_2)

def command_home(u1,u2):
    command = input("Now what would you like to do with these two numbers?\n").lower()
    if command == "add":
        calc_add(u1,u2)
    elif command == "subtract":
        calc_subtract(u1,u2)
    elif command == "multiply":
        calc_multiply(u1,u2)
    elif command == "divide":
        calc_divide(u1,u2)

def calc_add(user_input_1,user_input_2):
    add_result = (user_input_1 + user_input_2)
    print(add_result)

"""the rest of the functions go here, must be defined to take the inputs passed"""

startup_screen()

We have redefined command_home to take two objects as inputs (which should be the user_1 and user_2 from load_screen ). You could call them anything but I called them u1 and u2 so I wouldn't have to type so much. Now, command_home has these values and can, in turn, pass them into the functions which it calls that need them. We have also changed all of the function calls inside the if / elif block so that u1 and u2 are passed into those functions.

Then, we have redifined calc_add to take two inputs, and I called them the same as you did already inside the function, so I would have one less line to change - user_input_1 and user_input_2 .

Now when you ask for them to be added together into add_result , they exist and have the expected values, so everything now works.