Bit fields in python?

[geremy condra]

On Tue, Sep 7, 2010 at 9:53 PM, Eli Bendersky <eliben at gmail.com> wrote:
>>
>> I'm trying to rewrite a c program in python & encountered several
>> problems. I have some data structures in my c program like below:
>>
>> typedef struct
>> {
>>     unsigned short size;
>>
>>     unsigned short reserved:8;
>>     unsigned short var_a1:2;
>>     unsigned short var_a2:2;
>>     unsigned short var_a3:2;
>>     unsigned short var_a4:2;
>>
>>     unsigned int var_a5;
>> }structa;
>>
>>  typedef struct
>> {
>>     unsigned short size;
>>
>>     unsigned char reserved:4;
>>     unsigned char var_b1:1;
>>     unsigned char var_b2:1;
>>     unsigned char var_b3:1;
>>     unsigned char var_b4:1;
>>
>>     structa var_structa;
>> }structb;
>>
>> I tried to code the above in python but only got this far:
>>
>> class StructA(object):
>>     def __init__(self, size=0)
>>     self.size = size
>>
>> class StructB(object):
>>     def __init__(self, size=0)
>>
>> Any equivalent for c data structures & bit fields in python? And how do I
>> define var_structa (in structb) in python?
>>
>
> Bitfields are most commonly used for extreme space optimization - i.e.
> shoving several variables and flags with carefully limited ranges into a
> single work. In Python you rarely work this way (where such an optimization
> is warranted, Python isn't the best tool for the job). However, as in your
> use case, it is sometimes needed in Python in order to communicate with
> other devices over the network or some other link.
>
> In my work with Python and embedded devices I've found the construct library
> (http://construct.wikispaces.com/) very useful. It allows to you very easily
> define complex formats for frames/messages on the bit and byte level. The
> idea is to use construct to encode and decode messages being sent to an
> embedded device. It works great.
>
> If you have further questions about this approach, feel free to ask.
>
> Eli

That's really an excellent find. Thanks for bringing it up.

Geremy Condra