Segment tree implementation

import math

arr=[1,2,5,6,7,9]
n=len(arr)

def build_segment_tree(seg_tree,seg_idx,arr,left,right):
    if left==right:
        seg_tree[seg_idx]=arr[left]
        return seg_tree[seg_idx]

    mid=(left+right)//2
    left_sum=build_segment_tree(seg_tree,2*seg_idx+1,arr,left,mid)
    right_sum=build_segment_tree(seg_tree,2*seg_idx+2,arr,mid+1,right)
    seg_tree[seg_idx]=left_sum+right_sum
    return seg_tree[seg_idx]

def query(seg_tree,seg_idx,left,right,query_left,query_right):

    #complete overlap
    if left>=query_left and right<=query_right:
        return seg_tree[seg_idx]

    #no overlap
    if right<query_left or left>query_right:
        return 0

    mid=(left+right)//2
    return query(seg_tree,2*seg_idx+1,left,mid,query_left,query_right)+query(seg_tree,2*seg_idx+2,mid+1,right,query_left,query_right)

def update(seg_tree,seg_idx,left,right,diff,idx):

    if idx<left or idx>right:
        return

    seg_tree[seg_idx]+=diff
    if left!=right:
        mid=(left+right)//2
        update(seg_tree,2*seg_idx+1,left,mid,diff,idx)
        update(seg_tree,2*seg_idx+2,mid+1,right,diff,idx)



size=2*(1<<math.ceil(math.log2(n)))-1
seg_tree=[0]*size
build_segment_tree(seg_tree,0,arr,0,n-1)
print(seg_tree)
print(query(seg_tree,0,0,n-1,2,4))
new_value_at_3rd_idx=14
diff=new_value_at_3rd_idx-arr[3]
arr[3]=14
update(seg_tree,0,0,n-1,diff,3)