Construct is a powerful declarative parser (and builder) for binary
data.

Instead of writing imperative code to parse a piece of data, you
declaratively define a data structure that describes your data. As
this data structure is not code, you can use it in one direction to
parse data into Pythonic objects, and in the other direction, convert
(build) objects into binary data.

This is the Python 3 version of the package.