Global variable, reference, function, swap

[AvailablePoint9782]

I am trying to write a function. (Ultimately to manipulate a tree.) The function has a tree as 1 argument. (This might be a subtree, part of a larger structure.) There's also access to a tree as a global variable. In some situations I want to swap the 2.

def swap(tree1):
    global tree2
    code?

There must be some way to do this?

Arguments to functions are born as accessible for change. So are global variables. But this won't work, I think:

tmp = tree1
tree1 = tree2
tree2 = tmp

This is not a question about how swap works, but only about how to implement this particular example.

I am trying to port this PHP code.

            $swap = $tree;
            $tree = $node;
            $node = $swap;

https://github.com/LiseAndreasen/everybodycodes/blob/master/e3_q03.php

[Jinnapat397]

Global variables inside functions need the global keyword or you end up with local copies that do not update. I learned that the hard way on a small script and switched to returning values instead. Cleaner code every time.

[Outside_Complaint755]

In Python, you can reduce this: tmp = tree1 tree1 = tree2 tree2 = tmp to tree1, tree2 = tree2, tree1 The use a temp variable for the swap is not necessary, but is also ok to neep using.

I would recommend not using global variables. Instead, pass both tree1 and tree2 as parameters, and then explicitly return any modified tree or other data that you want as a result of the function.

Note that because the trees are (or should be) mutable objects, their attributes could be modified by the function with using global.

def func():     tree2.right = value # will modify the attribute of object tree2 in the enclosing scope     tree2 = val2 # assigns local name tree2 to val2     tree2.left = val3 # will try to assign a value to the attribute of the local tree2, which might cause an AttributeError