Pythonic ways to avoid Pointers

Question

Assume we have an object a and we want modify data which is structures like this

a.substructure1.subsubstructure1.name_of_the_data1

and this

a.substructure2.subsubstructure2.name_of_the_data2

To access this structure we call an external method get_the_data_shortcut(a) which is heavily parameterized (for example the parameter subsstructure specifies which substructure to return). This seems very redundant but there is a very good default setting for all these parameter which makes sense. Also, this function will return another branch of data if the default branch is not available.

How do I modify get_the_data_shortcut(a) ?

b = get_the_data_shortcut(a)
b = b + 1

Then, get_the_data_shortcut(a) is unchanged because well Python is not Java.

Do I need a setter? Mostly, this is not my code and written by people who write pythonic code, and I am trying to keep up with those standards.

The usual Python way would be to do something like b = a.substructure1.subsubstructure1; b.name_of_the_data1 += 1. But maybe you should write a minimal reproducible example so we have something more tangible to discuss. — PM 2Ring
– PM 2Ring, Commented Aug 28, 2015 at 16:01

Chad S. · Accepted Answer · 2015-08-28 17:05:57Z

1

As you discovered changing the object b refers to won't modify the a object (or its substructures). If you want to do this you will need a method similar to your get_the_data_shortcut(a). Namely a

set_the_data_shortcut(a, newvalue)

Alternatively you could have a method which would return the substructure the value was stored in and manipulate that..

# returns a.substructure2.subsubstructure2 
#          or a.substructure1.subsubstructure1 based on the value of kind
substruct = get_the_substructure(a, kind)
substruct.name_of_data1 += 1

answered Aug 28, 2015 at 17:05

Chad S.

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Comments

Fernando Matsumoto · Accepted Answer · 2015-08-28 16:10:25Z

1

Python uses reference types, just like java. However, when you do

b = b + 1

you are not updating the object you have. Instead, you are creating a new object and assigning it to the variable b.

If you want to update the value of b in the data structure, you should follow your suggestion and write a setter for the data structure.

answered Aug 28, 2015 at 16:10

Fernando Matsumoto

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