does lack of type declarations make Python unsafe?

Peter Hansen peter at
Tue Jun 17 04:10:34 CEST 2003

Ben Finney wrote:
> You, the programmer (or team of programmers) will never run the program
> the same way as the customer will, except by blind accident.  You can't
> know what the customer will do with it ahead of time, and neither can
> the customer.

Bonus: XP specifies an "on-site customer" who pretty much does just what
you suggest.

> Testing cannot try more than a miniscule fraction of the combination of
> inputs and usage that the customers will subject it to.  

Quite debatable.  Automated acceptance tests, by definition, cover the
bulk of the functionality that has been designed in, since the only
functionality that's supposed to be designed in (under XP) is that which
is *required* by the acceptance tests.  Anything not covered by tests
was therefore put added inappropriately by an over-zealous developer.
(Again, an obvious simplification, but not much of one.)

> Automated testing, carefully thought out, can increase this fraction
> significantly; but "run the software before you give it to the customer"
> is a laughably inferior way of finding bugs.

I agree, that would indeed be a laughable, not to mention ineffective, approach.


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