Construct (python library) 

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

The library provides both simple, atomic constructs (such as
integers of various sizes), as well as composite ones which allow
you form hierarchical structures of increasing complexity. Construct
features bit and byte granularity, easy debugging and testing, an
easy-to-extend subclass system, and lots of primitive constructs to
make your work easier:

 -Fields: raw bytes or numerical types
 -Structs and Sequences: combine simpler constructs into more complex
  ones
 -Adapters: change how data is represented
 -Arrays/Ranges: duplicate constructs
 -Meta-constructs: use the context (history) to compute the size of data
 -If/Switch: branch the computational path based on the context
 -On-demand (lazy) parsing: read only what you require
 -Pointers: jump from here to there in the data stream
 -Tunneling: prefix data with a byte count or compress it

Optional dependancies include Enum34, Numpy, and Arrow.