pystructs began with the desire to create a library that could handle bytes comfortably, such as the structure in c. It was because it was too hard to parse the bytes in python.

Therefore, it had to be easy for people to use when writing the fields. Furthermore, we hoped that there would be a function to handle variable bytes depending on the variable values.

So, in pystructs, write fields into Struct like model of django.
Also we can handle variable value in pystructs.