Applying pre and post conditions into python using decorators

pre and postconditions in python.py

# Pre and Post conditions in Java are done through comments a programmer puts 
# around methods, or by raising errors directly in a function. However,
# if a group of functions need the same pre and post conditions, copying and pasting code
# can get tedious. In Python this problem can be avoided through the use of 
# decorators. A template is laid out below:


def checkConditions(func):
	def wrapped(*args, **kwargs):
		if not (precondition_bool_expression):
			raise Exception(reason)
		else:
			result = func(*args, **kwargs)
			
			if not (postcondition_bool_expression):
				raise Exception(reason)
			else:
				return result
				
	return wrapped

# If you know what args and kwargs are going to be passed to func and have them
# explicitly laid out in the declaration of wrapped, yet you still want to use
# the decorator on a method inside of a class:

def checkConditions(func):
	def wrapped(self, arg1, arg2, arg3, etc):
		if not (precondition_bool_expression):
			raise Exception(reason)
		else:
			result = func(self, arg1, arg2, arg3, etc)
			
			if not (postcondition_bool_expression):
				raise Exception(reason)
			else:
				return result
				
	return wrapped

Thank you!