Passing variables between methods in Python?

Question

I have a class and two methods. One method gets input from the user and stores it in two variables, x and y. I want another method that accepts an input so adds that input to x and y. Like so:

class simpleclass(object):
    def getinput(self):
        x = input("input value for x: ")
        y = input("input value for y: ")
    def calculate(self, z):
        print(x + y + z)

When I run calculate(z) for some number z, it gives me errors saying the global variables x and y aren't defined.

How can calculate get access to the x and y values that were assigned in getinput?

Does this answer your question? How to share variables between methods in a class? — outis
– outis, Commented Dec 19, 2021 at 19:39
@outis it's close, but I decided this is the better version of the question to use as a canonical. — Karl Knechtel
– Karl Knechtel, Commented Oct 23, 2022 at 3:45

Karl Knechtel · Accepted Answer · 2022-08-17 06:36:05Z

17

These need to be instance variables:

class simpleclass(object):
    def __init__(self):
        self.x = None
        self.y = None

    def getinput(self):
        self.x = input("input value for x: ")
        self.y = input("input value for y: ")
   
    def calculate(self, z):
        print(self.x + self.y + z)

edited Aug 17, 2022 at 6:36

Karl Knechtel

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answered Mar 1, 2012 at 16:33

turtlebender

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1 Comment

Li-aung Yip Over a year ago

+1 for most correct answer illustrating use of the __init__() method.

Karl Knechtel · Accepted Answer · 2022-08-17 06:37:05Z

5

You want to use self.x and self.y. Like so:

class simpleclass(object):
    def getinput(self):
        self.x = input("input value for x: ")
        self.y = input("input value for y: ")
    def calculate(self, z):
        print(self.x + self.y + z)

edited Aug 17, 2022 at 6:37

Karl Knechtel

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answered Mar 1, 2012 at 16:32

Li-aung Yip

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Comments

Karl Knechtel · Accepted Answer · 2022-08-17 06:37:50Z

3

x and y are local variables. They get destroyed when you move out from the scope of that function.

class simpleclass(object):
    def getinput(self):
        self.x = input("input value for x: ")
        self.y = input("input value for y: ")
    def calculate(self, z):
        print(int(self.x) + int(self.y) + z)

edited Aug 17, 2022 at 6:37

Karl Knechtel

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answered Mar 1, 2012 at 16:34

Karoly Horvath

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1 Comment

DSM Over a year ago

Probably want to get a number from the string at some point if you're switching to raw_input.

Karl Knechtel · Accepted Answer · 2022-08-17 06:38:23Z

2

Inside classes, there's a variable called self you can use:

class Example(object):
    def getinput(self):
        self.x = input("input value for x: ")
    def calculate(self, z):
        print(self.x + z)

edited Aug 17, 2022 at 6:38

Karl Knechtel

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answered Mar 1, 2012 at 16:33

Brendan Long

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Comments

Karl Knechtel · Accepted Answer · 2022-08-17 06:40:03Z

class myClass(object):
    def __init__(self):
        pass
    
    def helper(self, jsonInputFile):
        values = jsonInputFile['values']
        ip = values['ip']
        username = values['user']
        password = values['password']
        return values, ip, username, password
    
    def checkHostname(self, jsonInputFile):
       values, ip, username, password = self.helper(jsonInputFile)
       print(values)
       print('---------')
       print(ip)
       print(username)
       print(password)

The __init__ method initializes the class. The helper function just holds some variables/data/attributes and releases them to other methods when you call it. Here jsonInputFile is some JSON. The checkHostname method logs in to some device/server to check the hostname; but it needs ip, username and password for that, which it gets by calling the helper method.

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