CODEWITHSUNDEEP
pythonmemory-management
rondo9
rondo9

Reputation: 113

Pointing to Address in Python

I am doing a form of breadth first search in a directed graph, and I want to store data recursively in the form (node, parent data*). How is this recursive? Starting with the root it will look like (root, None). Then the data for its child will be (child1, (root, None)). The child of child1 will then store (child2, (child1, (root, None))).

Obviously as the path length grows this becomes a lot of data. My question is: Lets say I assign a variable to the parent data, say parent_data = (root, None) and then write the child data as (child1, parent_data), is the variable storing all the parent data or is it simply a reference that will access the parent data upon request? I don't want to be storing all of this information multiple times.

What I wish I could do was simply have a C++ style pointer where in C++ notation I would assign tuple * parent_pointer = &(root, None).

Is this possible in Python or even necessary?

Apologies if the question is not clear, I am new to CS.

Upvotes: 0

Views: 44

Answers (2)

AbdealiLoKo
AbdealiLoKo

Reputation: 3337

If you're using lists, or tuples, or dict, or even any custom created class - to store the parent_data, it will use the pointer by default. i.e. it won't copy the data.

Example:

In []: parent_data = ['root', None]

In []: child_data = ['child1', parent_data]

In []: child_data
Out[]: ['child1', ['root', None]]

In []: child_data[1][1] = "THIS USED TO BE NONE"

In []: child_data
Out[]: ['child1', ['root', 'THIS USED TO BE NONE']]

In []: parent_data
Out[]: ['root', 'THIS USED TO BE NONE']

In []: id(parent_data)
Out[]: 4705828232

In []: id(child_data[1])
Out[]: 4705828232

To do a value based copy, you need to use: parent_data.copy()

Upvotes: 2

volcano
volcano

Reputation: 3582

Python variables are references to objects, this code

obj1 = obj2

will store a reference to obj2 in obj1 - you can check it with the help of id function.

The whole idea of Python "by reference" approach is to make issue of memory management mute

Upvotes: 1

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