'grabbing' local variables without a return

Question

I'm not entirely certain how to word it, but I'll explain what I'm looking to do.

def function(self):
    x = "x"
    y = "y"
    z = "z"

By creating this function as a unique object of a class I should be allocating memory to the variables themselves. How, at the time of creation of the class object and calling this function, can I get the variables directly from this function?

(i.e. class.function.x)

I'm not asking for return syntax, I want direct memory mapping (or calling) of this variable without returning a value.

As far as I know you can't - that is the point of a return. If you want them to be accessed by other methods on the same class - you can make new attributes of that class : ''self.x = "x"'', but once the function/method ends then the local variables dissapear — Tony Suffolk 66, May 09 '16 at 16:29
@Tony Suffolk 66 The point is direct memory mapping without segment faults, not make localized variables. I need the pointers, C pointers, at least as a start. — NationWidePants, May 10 '16 at 17:16
so use mmap - and actually directly allocate the memory. As the answers have given you - there is no direct way to access the memory of a local variable from outside the function. — Tony Suffolk 66, May 10 '16 at 17:22

score 1 · Answer 1 · answered May 09 '16 at 16:29

1

No. The scope is destroyed when the function returns, and all local variables along with it.

answered May 09 '16 at 16:29

Ignacio Vazquez-Abrams

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when it returns, yes, but what about at runtime? – NationWidePants May 09 '16 at 16:42
@NationWidePants: ... It returns during runtime, so I don't know what you're getting at. – Ignacio Vazquez-Abrams May 09 '16 at 17:07
Once the object (,object being the function called, in this case,) is created it instantiates the variables on a stack. Where'(s/re) the pointer(s)? Certainly not a trivial question, and not one most people ask since I doubt it's considered 'pythonic' to do or ask such a thing. – NationWidePants May 10 '16 at 17:28
There is no "stack" in Python, only the scope. And the variables don't exist until the function is called. – Ignacio Vazquez-Abrams May 10 '16 at 17:29

score 1 · Answer 2 · answered May 09 '16 at 16:30

I do not believe that those variables are instantiated until the function is run, and go out of scope when the functions returns. As posted I do not think what you want is possible (happy to be corrected).

However you can do,

class A(object):
    def f(self):
        pass
A.f.b = 42

when you make your class. Then later A.f.b is accessible.

totoro · Answer 3 · 2016-05-09T17:24:51.237

A basic method only remembers symbols, binding occurs upon invocation.

Python bindings 101

A class can bind variable, and so can an instance (object), and method invocation can change the instance and class variables.

http://ideone.com/KkzhRk

class Binder(object):
    x = "x"
    y = "y"
    z = "z"

    def f1(self):
        self.x = "xx"
        self.y = "yx"
        self.z = "zx"

    def f2(self):
        Binder.x = "xx"
        Binder.y = "yx"
        Binder.z = "zx"

binder = Binder()

print(Binder.x)  # class access
print(Binder.y)  # class access
print(Binder.z)  # class access
print(binder.x)  # instance access
print(binder.y)  # instance access
print(binder.z)  # instance access

binder.f1()

print(Binder.x)  # class access
print(Binder.y)  # class access
print(Binder.z)  # class access
print(binder.x)  # instance access
print(binder.y)  # instance access
print(binder.z)  # instance access

binder.f2()

print(Binder.x)  # class access
print(Binder.y)  # class access
print(Binder.z)  # class access
print(binder.x)  # instance access
print(binder.y)  # instance access
print(binder.z)  # instance access

There is also the topic of closures – nested method binding the values of the enclosing method.

http://ideone.com/bBnUJG

def mkclosure():
    x = "x"
    y = "y"
    z = "z"

    def closure():
        # Need to reference them for the closure to be created.
        return (x, y, z)

    return closure

function = mkclosure()

for cell in function.__closure__:
    print(cell.cell_contents)

'grabbing' local variables without a return

3 Answers3

Python bindings 101