status of Programming by Contract (PEP 316)?

[Carl Banks]

On Aug 30, 10:20 pm, al... at mac.com (Alex Martelli) wrote:
> Russ <uymqlp... 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?

Yes.

>  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,

Yes.

> 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.

Not really relevant, since there is no (or very little) dynamic memory
allocation.

Python really isn't suitable for in-flight controls for various
reasons, and mission critical concerns is a minor one (systems with
less underlying complexity tend to have fewer failure modes).  But
mostly it's raw throughput: Python is just too slow.  Flight control
computers have to be powerful enough make a ton of mathematical
calculations in a matter of milliseconds, and under strict weight and
power constraints.  The cost of running 100 times slower than optimal
is just too high.

At my current project, we're struggling with throughput even though we
use highly optimized code.  Python would be completely out of the
question.

Now, control towers don't have these constraints, and system failure
is not nearly as critical, so Python is a better option there.


Carl Banks