Recursions with nested lists

[sashiessay]

In your function, you have:

 sumtree+=add_tree(i) 

That is equivalent to:

 sumtree = sumtree + add_tree(i) 

Given that you want to replace a and b in a + b, what matches from your earlier code?

Thank you for the push. I ended up writing this

def op_tree(tree, op, base_case):
    """
    Recursively runs a given operation on tree leaves.
    Return type depends on the specific operation.

    Inputs
       tree: A list (potentially containing sublists) that
       represents a tree structure.
       op: A function that takes in two inputs and returns the
       result of a specific operation on them.
       base_case: What the operation should return as a result
       in the base case (i.e. when the tree is empty).
    """  
  
    if isinstance(tree,int):
        return op(base_case,tree)
        
    else:
        value=op(base_case,base_case)
        for i in tree:
            value+=op_tree2(i,op,base_case)
        return value

Which worked for the summation operation, but does not work for a product operation and I knew it was because I was using +=, which doesn't work for multiplication. However, going back to your comment after I tried this clarified things. I changed the code above incorporating your hint and I got it to work!