Pycom FiPy, Руководство пользователя, Страница: 348 / 496

uctypes – Access Binary Data in a
Structured Format
This module implements "foreign data interface" for MicroPython. The idea behind it is
similar to CPython’s
ctypes
modules, but the actual API is different, streamlined and
optimised for small size. The basic idea of the module is to define data structure layout with
about the same power as the C language allows, and the access it using familiar dot-syntax
to reference sub-fields.
Module ustruct Standard Python way to access binary data structures (doesn’t scale
well to large and complex structures).
Defining Structure Layout
Structure layout is defined by a "descriptor" - a Python dictionary which encodes field names
as keys and other properties required to access them as associated values. Currently,
uctypes
requires explicit specification of offsets for each field. Offset are given in bytes from
a structure start.
Following are encoding examples for various field types:
Scalar types:
"field_name" : uctypes.UINT32 | 0
In other words, value is scalar type identifier OR-ed with field offset (in bytes) from the start
of the structure.
Recursive structures:
"sub" : ( 2 , {
"b0" : uctypes.UINT8 | 0 ,
"b1" : uctypes.UINT8 | 1 ,
})
I.e. value is a 2-tuple, first element of which is offset, and second is a structure descriptor
dictionary (note: offsets in recursive descriptors are relative to a structure it defines).
Arrays of Primitive Types:
5.3.2 uctypes
348