Programming Forums > Script Programming > Python

coldDeath · Aug 9th, 2005, 2:32 AM

OK, i am making a simple program in python, all was going well until the variables didnt work. The actual code is a bit to long to post and it is very messy, so i made this example of what error i am getting.

(Toggle Plain Text)

#defining the variable
msg = "Hello"
#function to chnage the msg variable to the argument in the funtion
def changeit(new):
	msg = new
	return msg
#calling the function with the argument "goodbye"
changeit("Goodbye")
#Printing the variable to check that it has changed acording to the function that we called
print msg

You see basically, i have declared a variable, i then have made a funtion that should change that variable, i then call that funtion and print the variable.

Basically, the msg variable stays as "Hello" and doesnt change. I think it is something to do with Global variables etc. but im not sure how to correct it, i tried return msg but it doesn't work.

I have searched google (maybe i am searching for the wrong words?) and i checked the python documentation but i cannot find the answer to my question.

How can i fix it so that it prints the variable from the function?

Dietrich · Aug 9th, 2005, 8:26 AM

You have a function that returns something so you need to assign it to a variable when you call it. This should do it:

(Toggle Plain Text)

#defining the variable
msg = "Hello"
#function to change the msg variable to the argument in the funtion
def changeit(new):
	msg = new
	return msg
#calling the function with the argument "goodbye"
msg = changeit("Goodbye")
#Printing the variable to check that it has changed acording to the function that we called
print msg

Sane · Aug 9th, 2005, 8:27 AM

(Toggle Plain Text)

#defining the variable
msg = "Hello"
#function to chnage the msg variable to the argument in the funtion
def changeit(new):
	msg = new
	return msg
#calling the function with the argument "goodbye"
msg = changeit("Goodbye")    #This line was changed
#Printing the variable to check that it has changed acording to the function that we called
print msg

Return from a function returns the variable to whatever called the function. The way you had it setup, the new value wasn't being returned to any variable, and the temporary variables were therefore not used.

For this part:

(Toggle Plain Text)

def changeit(new):
	msg = new
	return msg

Could be made:

(Toggle Plain Text)

def changeit(new):
	return new

Because declaring msg doesn't do anything anyways. Inside a function, only the variables that were changed and created within that function will operate, none will exist outside that function or the next time you visit the function again. The only way to ever see it again is with the command global, or using return and then passing it back as a paramater.

Here is another way of looking at your program that is slightly more advanced:

(Toggle Plain Text)

class variable(object): #variable can be changed to any word

    #this will initiate upon declaring variable
    def __init__(self, dec_variable):

        #self is the collection of variables within the class, dec_variable is the paramater passed when the class is declared
        self.text = dec_variable #self makes the variable able to be manipulated within the class, self.text = dec_variable is making "Hello" accessable by the other functions in this class

    def changeit(self, new_variable):

        #self is the collection of variables within the class, new_variable is the paramater passed when changeit is called
        self.text = new_variable #self.text which was declared in a different function, can still be manipulated here. It is redeclared as "Goodbye"


#Declare msg as a reference of the class variable
msg = variable("Hello")

#Access the function changeit in the class variable (since variable is referenced with msg)
msg.changeit("Goodbye")

#Print the variable variable.text (since variable is referenced with msg)
print msg.text

coldDeath · Aug 9th, 2005, 9:23 AM

Thanks for your help, just after i posted this topic, "the python bible" book form amazon.co.uk got delivered and i learnt how to do object oriented python, so i managed to sort out my problem.

It was a stupid error to make in the first place, thanks dietrich for sorting that out.
Sane that advanced way looks good, mine looks a bit like that

Sane · Aug 9th, 2005, 12:35 PM

Hey I sorted it out too! Just 30 seconds after dietrich did .

Aug 9th, 2005, 2:32 AM	#1
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	Variables OK, i am making a simple program in python, all was going well until the variables didnt work. The actual code is a bit to long to post and it is very messy, so i made this example of what error i am getting. (Toggle Plain Text) #defining the variable msg = "Hello" #function to chnage the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" changeit("Goodbye") #Printing the variable to check that it has changed acording to the function that we called print msg #defining the variable msg = "Hello" #function to chnage the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" changeit("Goodbye") #Printing the variable to check that it has changed acording to the function that we called print msg You see basically, i have declared a variable, i then have made a funtion that should change that variable, i then call that funtion and print the variable. Basically, the msg variable stays as "Hello" and doesnt change. I think it is something to do with Global variables etc. but im not sure how to correct it, i tried return msg but it doesn't work. I have searched google (maybe i am searching for the wrong words?) and i checked the python documentation but i cannot find the answer to my question. How can i fix it so that it prints the variable from the function?

Aug 9th, 2005, 8:26 AM	#2
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	You have a function that returns something so you need to assign it to a variable when you call it. This should do it: (Toggle Plain Text) #defining the variable msg = "Hello" #function to change the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" msg = changeit("Goodbye") #Printing the variable to check that it has changed acording to the function that we called print msg #defining the variable msg = "Hello" #function to change the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" msg = changeit("Goodbye") #Printing the variable to check that it has changed acording to the function that we called print msg __________________ I looked it up on the Intergnats!

Aug 9th, 2005, 8:27 AM	#3
Sane Programming Guru Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,028 Rep Power: 6	(Toggle Plain Text) #defining the variable msg = "Hello" #function to chnage the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" msg = changeit("Goodbye") #This line was changed #Printing the variable to check that it has changed acording to the function that we called print msg #defining the variable msg = "Hello" #function to chnage the msg variable to the argument in the funtion def changeit(new): msg = new return msg #calling the function with the argument "goodbye" msg = changeit("Goodbye") #This line was changed #Printing the variable to check that it has changed acording to the function that we called print msg Return from a function returns the variable to whatever called the function. The way you had it setup, the new value wasn't being returned to any variable, and the temporary variables were therefore not used. For this part: (Toggle Plain Text) def changeit(new): msg = new return msg def changeit(new): msg = new return msg Could be made: (Toggle Plain Text) def changeit(new): return new def changeit(new): return new Because declaring msg doesn't do anything anyways. Inside a function, only the variables that were changed and created within that function will operate, none will exist outside that function or the next time you visit the function again. The only way to ever see it again is with the command global, or using return and then passing it back as a paramater. Here is another way of looking at your program that is slightly more advanced: (Toggle Plain Text) class variable(object): #variable can be changed to any word #this will initiate upon declaring variable def __init__(self, dec_variable): #self is the collection of variables within the class, dec_variable is the paramater passed when the class is declared self.text = dec_variable #self makes the variable able to be manipulated within the class, self.text = dec_variable is making "Hello" accessable by the other functions in this class def changeit(self, new_variable): #self is the collection of variables within the class, new_variable is the paramater passed when changeit is called self.text = new_variable #self.text which was declared in a different function, can still be manipulated here. It is redeclared as "Goodbye" #Declare msg as a reference of the class variable msg = variable("Hello") #Access the function changeit in the class variable (since variable is referenced with msg) msg.changeit("Goodbye") #Print the variable variable.text (since variable is referenced with msg) print msg.text class variable(object): #variable can be changed to any word #this will initiate upon declaring variable def __init__(self, dec_variable): #self is the collection of variables within the class, dec_variable is the paramater passed when the class is declared self.text = dec_variable #self makes the variable able to be manipulated within the class, self.text = dec_variable is making "Hello" accessable by the other functions in this class def changeit(self, new_variable): #self is the collection of variables within the class, new_variable is the paramater passed when changeit is called self.text = new_variable #self.text which was declared in a different function, can still be manipulated here. It is redeclared as "Goodbye" #Declare msg as a reference of the class variable msg = variable("Hello") #Access the function changeit in the class variable (since variable is referenced with msg) msg.changeit("Goodbye") #Print the variable variable.text (since variable is referenced with msg) print msg.text __________________ Looking for tough programming challenges? Try participating in Sane's Monthly Algorithms Challenges! Composing Techno is a little side hobby of mine. Techno by DJ Sane. All free for download.

Aug 9th, 2005, 12:35 PM	#5
Sane Programming Guru Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,028 Rep Power: 6	Hey I sorted it out too! Just 30 seconds after dietrich did . __________________ Looking for tough programming challenges? Try participating in Sane's Monthly Algorithms Challenges! Composing Techno is a little side hobby of mine. Techno by DJ Sane. All free for download.

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Aug 9th, 2005, 9:23 AM	#4
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 4	Thanks for your help, just after i posted this topic, "the python bible" book form amazon.co.uk got delivered and i learnt how to do object oriented python, so i managed to sort out my problem. It was a stupid error to make in the first place, thanks dietrich for sorting that out. Sane that advanced way looks good, mine looks a bit like that

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Programming Forums > Script Programming > Python

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