[Tutor] decorators in a class

[anish singh]

Trying to use decorators in my class. I am calling
build_tree from the main function and i want to increment
the arguments by a constant factor by using decorators.
However as build_tree is a recursive function, I don't want
to call it recursively with increased constant factor always.

Probably decorators are not the ideal way for this but still
how to go about it using decorators.

Simple solution would be to just pass the parameters after
incrementing with constant values in the main function.
However, I want the caller of build_tree to not know that
internally we increment the indexes in the class and work
on that.
I can also call a intermediate function and then call build_tree
but then would that be the right way?

def pow_of_2(n):
    n -= 1
    n |= n >> 1
    n |= n >> 2
    n |= n >> 4
    n |= n >> 8
    n |= n >> 16
    n += 1
    return n

def p_decorate(func):
    def func_wrapper(self, left, right, root):
        return func(self, left+self.n, right+self.n, root)
    return func_wrapper

class segment_tree(object):
    def __init__(self, data):
        self.n = pow_of_2(len(data))
        self.tree = [0]*self.n + data + [0]*(self.n - len(data))

    @p_decorate
    def build_tree(self, left, right, root):
        if left == right:
            return self.tree[left]
        #below build_tree should not use decorated function,
        #how to achieve that?
        s = self.build_tree(left, (left+right)/2, 2*root) +
                  self.build_tree(1+(left+right)/2, right, 2*root+1)
        self.tree[root] = s

    def __repr__(self):
        return " ".join(str(i) for i in self.tree)

data = [1, 2, 3, 4]
sg = segment_tree(data)
sg.build_tree(0, 7, 1)
print(sg)