pre/post-condition support?

[Martin von Loewis]

"Greg Wilson" <gvwilson at nevex.com> writes:

> Has anyone experimented with Python extensions to support programming by
> contract (pre/post conditions on methods + state assertions that are
> respected by inheritance)?  If so, I'd welcome pointers.

As for pre/post conditions and state assertions: with Python 1.5.x,
there is the assert statement:

class Data:
  def __init__(self):self.items = {}
  def add(self,key,value):
    assert (not self.items.has_key(key))
    self.items[key] = value

d = Data()
d.add("milk","white")
d.add("milk","white")

As for respecting inheritance: I guess approaches taken in other
languages work in Python as well:

class Base:
  def method(self,params):
    assert preconditions
    result = self.method_implementation(self,params)
    assert postconditions
    return result

You can probably apply a number of reflection-based tricks in Python;
I doubt that this would make your code more understandable.

Regards,
Martin