CODEWITHSUNDEEP
pythonpython-2.7tornado
user94628
user94628

Reputation: 3731

Making a variable cross module in Python - Within a class and function

I'm trying to use a variable in other python modules, like this:

In a.py:

class Names:
    def userNames(self):
        self.name = 'Richard'

In z.py:

import a
d = a.Names.name
print d

However this doesn't recognise the variable name and the following error is received:

AttributeError: type object 'Names' has no attribute 'name'

Thanks

Upvotes: 0

Views: 1887

Answers (3)

Useless
Useless

Reputation: 67842

There are lots of different scopes a variable can be bound to, which is what you seem to be confused about. Here are a few:

# a.py
a = 1 # (1) is module scope

class A:
    a = 2 # (2) is class scope

    def __init__(self, a=3): # (3) is function scope
        self.a = a           # (4) self.a is object scope

    def same_as_class(self):
        return self.a == A.a # compare object- and class-scope variables

    def same_as_module(self):
        return self.a == a   # compare object- and module-scope variables

Now see how these different variables (I only called them all a to make the point, please don't do this for real) are named, and how they all have different values:

>>> import a
>>> a.a
1 # module scope (1)
>>> a.A.a
2 # class scope (2)
>>> obj1 = a.A() # note the argument defaults to 3 (3)
>>> obj1.a       # and this value is bound to the object-scope variable (4)
3
>>> obj.same_as_class()
False             # compare the object and class values (3 != 2)

>>> obj2 = a.A(2) # now create a new object, giving an explicit value for (3)
>>> obj2.same_as_class()
True

Note we can also change any of these values:

>>> obj1.same_as_module()
False
>>> obj1.a = 1
>>> obj1.same_as_module()
True

For reference, your z.py above should probably look like:

import a
n = a.Names()
d.userNames()
d = n.name
print d

because a.Name is a class, but you're trying to refer to an object-scope variable. An object is an instance of a class: I've called my instance n. Now I have an object, I can get at the object-scope variable. This is equivalent to Goranek's answer.

In terms of my previous example, you were trying to access obj1.a without having an obj1 or anything like it. I'm not really sure how to make this clearer, without turning this into an introductory essay on OO and Python's type system.

Upvotes: 4

Goranek
Goranek

Reputation: 896

file:a.py

class Names:
    def userNames(self):
        self.name = 'Richard'

file:z.py

import a
c = a.Names()
c.userNames()
what_you_want_is = c.name

Btw, this code makes no sense..but this is apparently what you want

Better a.py

class Names:
    def userNames(self, name):
        self.name = name

Better z.py

import a
c = a.Names()
c.userNames("Stephen or something")
what_you_want_is = c.name 
# what_you_want_is is "Stephen or something"

Upvotes: 3

Marcin
Marcin

Reputation: 49886

"I've checked again and it's because I'm importing from is a Tornado Framework and the variable is within a class."

Accordingly, your problem is not the one shown in your question.

If you actually want to access the variable of a class (and likely, you don't), then do this:

from othermodule import ClassName

print ClassName.var_i_want

You probably want to access the variable as held inside an instance:

from othermodule import ClassName, some_func

classnameinstance = some_func(blah)
print classnameinstance.var_i_want

Update Now that you have completely changed your question, here is the answer to your new question:

IN this code:

class Names:
    def userNames(self):
        name = 'Richard'

name is not a variable accessible outside of the activation of the method userNames. This is known as a local variable. You would create an instance variable by changing the code to:

def userNames(self):
        self.name = 'Richard'

Then, if you have an instance in a variable called classnameinstance you can do:

print classnameinstance.name

This will only work if the variable has been already created on the instance, as by calling userNames.

You don't need to import the class itself if there is some other way to receive instances of the class.

Upvotes: 4

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