A class for C-like structuures in Python

[Thomas Gagne]

OK.  So they really aren't C structures, but they're close.

Now, I've only been programming in Python for about two days, so naturally I'm
an expert.

My little how-to-learn-Python project is to build a Python interface to my
open-source middleware project, isectd.  In the front of every packet over the
wire is a structure called IsdHeader.  Client and worker programs sometimes
look at this structure for different reasons (mostly it's used by the
middleware daemon).

ANYWAY (it's a song about Alice) I needed to recreate the structure in Python
and found myself creating a lot of things that should be generally useful, so
I created a class called CStructure which I can use as a super for the
subclass IsdHeader.

To wit the attachments...

The file, IsdHeader.py, is an example of how a subclass may use it. Basically
it calls the super with a tuple of tuples describing the members and their
format (for the struct module).  CStructure uses the tuples to build a
dictionary to hold the values until the programmer requests the structure as a
string (asBytes()).
-------------- next part --------------
import struct

class CStructure:
	def __init__(self, theTuples):
		self.fmt = ''
		self.members = {}
		self.shape = theTuples

		for n,f in self.shape:
			self.members[n] = None
			self.fmt = self.fmt + f

	def getMember(self, name):
		if (self.members.has_key(name)):
			return self.members[name]

	def setMember(self, name, value):
		if (self.members.has_key(name)):
			self.members[name] = value;
			return self.members[name]

	def getFormat(self):
		return self.fmt

	def __len__(self):
		return struct.calcsize(self.fmt)

	def asBytes(self):
		self.bytes = ''

		for n,f in self.shape:
			if f[-1] == 'x':
				self.bytes = self.bytes + struct.pack(f)
			else:
				self.bytes = self.bytes + struct.pack(f, self.members[n])

		return self.bytes
-------------- next part --------------
import isdio
from CStructure import *

class IsdHeader(CStructure):
	def __init__(self):
		CStructure.__init__(self, (
			('len','l'),
			('sequence','l'),
			('reply','h'),
			('error','h'),
			('command','h'),
			('version','h'),
			('workerid','l'),
			('more','h'),
			('fill','42x')))

		self.setMember('len', 0)
		self.setMember('sequence', 0)
		self.setMember('reply', 0)
		self.setMember('error', 0)
		self.setMember('command', 0)
		self.setMember('version', 0)
		self.setMember('workerid', 0)
		self.setMember('more', 0)