Clarity vs. code reuse/generality

[Scott David Daniels]

Paul Rubin wrote:
> Invalid input data is not considered impossible and doesn't imply a
> broken program, so assert statements are not the appropriate way to
> check for it.  I like to use a function like
> 
>   def check(condition, msg="data error"):
>      if not condition: raise ValueError, msg
> 
>   ... 
>   check (x >= 0, "invalid x")  # raises ValueError if x is negative
>   y = sqrt(x)

And I curse such uses, since I don't get to see the troublesome value,
or why it is troublesome.  In the above case, y = sqrt(x) at least
raises ValueError('math domain error'), which is more information than
you are providing.

How about:

      ...
      if x >= 0: raise ValueError('x = %r not allowed (negative)?' % x)
      ...

--Scott David Daniels
Scott.Daniels at Acm.Org