Pre/Postconditions with decorators

[Rittersporn]

My humble attempt to model pre/postconditions with 
decorators :-) It's also my first experiment 
with decorators. 
  If you have any ideas or thoughts on how to 
improve the code snippet, I'll be happy to  
learn more.

Enjoy :-)
 
def condition(pretext,posttext=""):
	precode=compile(pretext or "True","","eval")
	postcode=compile(posttext or "True","","eval")

	# function -> decorated(function)
	def decorate_condition(function):
		# FIXME: Does not work with wrapped functions
		argcount=function.func_code.co_argcount
		var=function.func_code.co_varnames[0:argcount]

		 # arguments -> closure(assertion)
		def evaluate_condition(*args,**kargs):
			# FIXME: check if "var" always contains ordered list of arguments
			# map arguments and
			args_seq=[(argname,args[pos]) for pos,argname in enumerate(var)]
			# key-arguments to value
			kargs_seq=[(k,v) for k,v in kargs.itervalues()]
			environment=args_seq+kargs_seq

			# precondition
			assert eval(precode,{},dict(environment)),pretext
			tmp=function(*args,**kargs)
			environment2=environment+[('result',tmp)]

			# postcondition
			assert eval(postcode,{},dict(environment2)),posttext
			return tmp

		return  evaluate_condition

	return decorate_condition

@condition("number>0 and number<2","result>=0")
def sqrt(number):
	import math
	return math.sqrt(number)

@condition("list(seq) is not None","sum(seq)==result")
def my_sum(seq):
	tmp=0
	for element in seq:
		tmp+=element
	return tmp

print sqrt(1.2)
print my_sum([1,2,3])