Steven Bethard wrote: > [EMAIL PROTECTED] wrote: > > However, is there a good reason why default parameters aren't evaluated > > as the function is called? (apart from efficiency and backwards > > compatibility)? > > So, one of my really common use cases that takes advantage of the fact > that default parameters are evaluated at function definition time: > > def foo(bar, baz, matcher=re.compile(r'...')): > ... > text = matcher.sub(r'...', text) > ... >
Surely "re.compile(r'...')" is effectively a constant ? So your above code is equivalent to : aConst = re.compile(r'...') def foo(bar, baz, matcher=aConst): ... text = matcher.sub(r'...', text) ... I agree that dynamic evaluation of default arguments seems much more pythonic, as well as getting rid of a common python gotcha. Regards, Fuzzy http://www.voidspace.org.uk/python/index.shmtl > If default parameters were evaluated when the function was called, my > regular expression would get re-compiled every time foo() was called. > This would be inefficient, especially if foo() got called a lot. If > Python 3000 changed the evaluation time of default parameters, I could > rewrite this code as: > > class foo(object): > matcher=re.compile(r'...') > def __new__(self, bar, baz, matcher=None): > if matcher is None: > matcher = self.matcher > ... > text = matcher.sub(r'...', text) > ... > > But that seems like a lot of work to do something that used to be pretty > simple... > > Steve -- http://mail.python.org/mailman/listinfo/python-list
