Should asserts be disabled in production?

I used to be quite annoyed by Perl CPAN's

Carp::Assert: "assert(...) if DEBUG;"

i.e. by the fact that you have to append "if DEBUG" to an assertion in order to get it disabled in production.



Now, I have flipped.



I often want assertions enabled in production code. At least cheap assertions.  In fact, I might go so far as to say "assertions should be enabled in production code by default, unless you explicitly say not to".



In which case, the Perl Carp::Assert syntax is not totally unreasonable.



I might prefer the Pythonish



if DEBUG: assert(...)



so that you can see the "if DEBUG" right up front.



But then again, Python's assert is disabled when you run Python "optimized" via python -O.



I was somewhat flabbergasted when I encountered Python style guides that recommended not using asserts, or specifically not using asserts inside library functions.    (Can't find a reference right now, so perhaps this is rare advice.)



Reason: since Python assert is disabled when you run optimized -O (which is common in some worlds), and since libraries cannot be sure that somebody competent is calling them, libraries should do

if !valid(parameter): raise someException

rather than

assert valid(parameter)

This advice is accurate, but unfortunate.  I always prefer concise code, and "assert" is more concise than "if...raise".   And probably less fragile, since exception hierarchies have a habit of changing.





So I can't blame Python, but I can still regret it.