status of Programming by Contract (PEP 316)?

[Alex Martelli]

Russ <uymqlp502 at sneakemail.com> wrote:
   ...
> programs." Any idea how much Python is used for flight control systems
> in commercial
> transport aircraft or jet fighters?

Are there differences in reliability requirements between the parts of
such control systems that run on aircraft themselves, and those that run
in airports' control towers?  Because Python *IS* used in the latter
case, cfr <http://www.python.org/about/success/frequentis/> ... if
on-plane control SW requires hard-real-time response, that might be a
more credible reason why Python would be inappropriate (any garbage
collected language is NOT a candidate for hard-real-time SW!) than your
implied aspersions against Python's reliability.

According to
<http://uptime.pingdom.com/site/month_summary/site_name/www.google.com>,
Google's current uptime is around 99.99%, with many months at 100% and a
few at 99.98% -- and that's on *cheap*, not-that-reliable commodity HW,
and in real-world conditions where power can go away, network cables can
accidentally get cut, etc.  I'm Uber Tech Lead for Production Systems at
Google -- i.e., the groups I uber-lead are responsible for some software
which (partly by automating things as much as possible) empowers our
wondrous Site Reliability Engineers and network specialists to achieve
that uptime in face of all the Bad Stuff the world can and does throw at
us.  Guess what programming language I'm a well-known expert of...?


> The important question is this: why do I waste my time with bozos like
> you?

Yeah, good question indeed, and I'm asking myself that -- somebody who
posts to this group in order to attack the reliability of the language
the group is about (and appears to be supremely ignorant about its use
in air-traffic control and for high-reliability mission-critical
applications such as Google's "Production Systems" software) might well
be considered not worth responding to.  OTOH, you _did_ irritate me
enough that I feel happier for venting in response;-)

Oh, FYI -- among the many tasks I undertook in my quarter-century long
career was leading and coordinating pilot projects in Eiffel for one
employer, many years ago.  The result of the pilot was that Eiffel and
its DbC features didn't really let us save any of the extensive testing
we performed for C++-coded components, and the overall reliability of
such extensively tested components was not different in a statistically
significant way whether they were coded in C++ or Eiffel; Eiffel did let
us catch a few bugs marginally earlier (but then, I'm now convinced
that, at that distant time, we used by far too few unit-tests for early
bug catching and relied too much on regression and acceptance tests),
but that definitely was _not_ enough to pay for itself.  DbC and
allegedly rigorous compile-time typechecking (regularly too weak due to
Eiffel's covariant vs countervariant approach, btw...), based on those
empirical results, appear to be way overhyped.

A small decorator library supporting DbC would probably be a nice
addition to Python, but it should first prove itself in the field by
being released and supported as an add-on and gaining wide acceptance:
"arguments" such as yours are definitely NOT going to change that.


Alex