Python: Getting value from calling function

Question

In Python, is there a simple way for an invoked function to get a value from the calling function/class ? I'm not sure if I'm phrasing that right, but I'm trying to do something like this:

class MainSection(object):
    def function(self):
        self.var = 47  # arbitrary variable 
        self.secondaryObject = secondClass()  # Create object of second class
        self.secondaryObject.secondFunction(3)  # call function in that object

and

class secondClass(object):
    def secondFunction(self, input)
        output = input + self.var  # calculate value based on function parameter AND variable from calling function
        return output
        #Access self.var from MainSection

This might be my lack of knowledge about Python, but I'm having a hard time finding a clear answer here. Is the best way to do that just passing the variable I want in as another second parameter to the second class? These are in separate files, if that makes a difference.

Where exactly are you trying to access self.var from the second function? You can just pass self.var when calling it like this: self.secondaryObject.secondFunction(self.var) — Jab
– Jab, Commented Dec 5, 2018 at 17:48

Rob Bricheno · Accepted Answer · 2018-12-05 17:55:32Z

2

Is the best way to do that just passing the variable I want in as another second parameter to the second class?

Yes, especially if there's only a transient relationship between the objects:

class secondClass(object):
    def secondFunction(self, input, var_from_caller)
        output = input + var_from_caller  # calculate value based on function parameter AND variable from calling function
        return output

You can even pass around the whole object if you like:

class secondClass(object):
    def secondFunction(self, input, calling_object)
        output = input + calling_object.var  # calculate value based on function parameter AND variable from calling function
        return output

If the relationship is more permanent, you could consider storing references to the related objects in instance variables:

class MainSection(object):
    def function(self):
        self.var = 47  # arbitrary variable 
        self.secondaryObject = secondClass(self)  # Create object of second class
        self.secondaryObject.secondFunction(3)  # call function in that object

...
class secondClass(object):
    def __init__(self, my_friend):
        self.related_object = my_friend

    def secondFunction(self, input)
        output = input + self.related_object.var  # calculate value based on function parameter AND variable from calling function
        return output
        #Access self.var from MainSection

edited Dec 5, 2018 at 17:55

answered Dec 5, 2018 at 17:47

Rob Bricheno

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2 Comments

Jab Over a year ago

Nice answer, also consider adding my example from my comment as well. Goes along with what he's asking and what you're saying as well

Rob Bricheno Over a year ago

@Jaba sure, I added an example for just passing around the variable too. Thanks for the feedback.

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