here's the head that i commented:
def iterate(self):
# this function is the guts of a class that wraps a tree root record
# indexing binary data on a blockchain. it is intended to yield the
# chunks in order when called.
# the number of bytes that have been yielded, increased every chunk
stream_output_offset = 0
# the size of all the chunks: the sum of the sizes of each child node
total_size = len(self)
