> http://www.wayforward.net/pycontract/pep-0999.html
I think another issue with using doc strings in this way
is that you are overloading a feature visible to end users.
If I look at the doc string then I would expect to be confused the result:
>>> help(circbuf)
Help on class circbuf in module __main__:
class circbuf
| Methods defined here:
|
| get(self)
| Pull an entry from a non-empty circular buffer.
|
| pre: not self.is_empty()
| post[self.g, self.len]:
| __return__ == self.buf[__old__.self.g]
| self.len == __old__.self.len - 1
| ...
Way to cryptic even for me :-)
I think you could get the same effect by overloading property
so you could make methods "smart" about pre and post conditions
The following is a first quick hack at it...:
class eiffel(property):
"""eiffel(method,precondition,postcondition)
Implement a Eiffel style method that enforces pre-
and post- conditions. I guess you could turn this
on and off if you wanted...
class foo:
def pre(self): assert self.x > 0
def post(self): assert self.x > 0
def increment(self):
self.x += 1
return
increment = eiffel(method,precondition,postcondition)
"""
def __init__(self,method,precondition,postcondition,doc=None):
self.method = method
self.precondition = precondition
self.postcondition = postcondition
super(eiffel,self).__init__(self.__get,None,None,doc)
return
def __get(self,this):
class funny_method:
def __init__(self,this,method,precondition,postcondition):
self.this = this
self.method = method
self.precondition = precondition
self.postcondition = postcondition
return
def __call__(self,*args,**kw):
self.precondition(self.this)
value = self.method(self.this,*args,**kw)
self.postcondition(self.this)
return value
return funny_method(this,self.method,self.precondition,self.postcondition)
class circbuf:
def __init__(self):
self.stack = []
return
def _get_pre(self):
assert not self.is_empty()
return
def _get_post(self):
assert not self.is_empty()
return
def _get(self):
"""Pull an entry from a non-empty circular buffer."""
val = self.stack[-1]
del self.stack[-1]
return val
get = eiffel(_get,_get_pre,_get_post)
def put(self,val):
self.stack.append(val)
return
def is_empty(self):
return len(self.stack) == 0
B = circbuf()
B.put('hello')
print B.get()
# Will bomb...
print B.get()
--
Patrick Miller | (925) 423-0309 | http://www.llnl.gov/CASC/people/pmiller
If you think you can do a thing or think you can't do a thing, you're
right. -- Henry Ford
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