import struct

class Struct(object):
	__slots__ = ('__attrs__', '__values__', '__def__', '__size__', '__cooked__')
	int8 = ('b', 1)
	uint8 = ('B', 1)
	
	int16 = ('h', 2)
	uint16 = ('H', 2)
	
	int32 = ('l', 4)
	uint32 = ('L', 4)
	
	float = ('f', 4)
	
	def __init__(self):
		self.__attrs__ = []
		self.__values__ = {}
		self.__def__ = ''
		self.__size__ = 0
		self.__cooked__ = False
	
	def __setattr__(self, name, value):
		if name in self.__slots__:
			return object.__setattr__(self, name, value)
		
		if self.__cooked__ == False:
			self.__def__ += value[0]
			self.__size__ += value[1]
			self.__attrs__.append(name)
			self.__values__[name] = 0
		else:
			self.__values__[name] = value
	
	def __getattr__(self, name):
		return self.__values__[name]
	
	def __cook__(self):
		self.__cooked__ = True
		return self
	
	def unpack(self, str):
		values = struct.unpack(self.__def__, str[:self.__size__])
		i = 0
		for name in self.__attrs__:
			self.__values__[name] = values[i]
			i += 1
		
		return self
	
	def pack(self):
		values = [self.__values__[name] for name in self.__attrs__]
		return struct.pack(self.__def__, *values)

if __name__=='__main__':
	class TestStruct(Struct):
		def __init__(self):
			Struct.__init__(self)
			
			self.foo, self.bar = Struct.uint32, Struct.float
			
			self.__cook__()
	
	test = TestStruct()
	test.unpack('\xEF\xBE\xAD\xDE\x00\x00\x80\x3F')
	assert test.foo == 0xDEADBEEF
	assert test.bar == 1.0
	
	test.foo = 0xCAFEBABE
	test.bar = 0.0
	assert test.pack() == '\xBE\xBA\xFE\xCA\0\0\0\0'