On Tue, 07 Sep 2010 12:40:57 +1000, Ben Finney wrote: > Steven D'Aprano <steve-remove-t...@cybersource.com.au> writes: > >> On Tue, 07 Sep 2010 11:00:45 +1000, Ben Finney wrote: >> >> > If you're going to use the list of float objects, you can convert >> > them all with a list comprehension. >> [...] >> > >>> numbers_as_float = [float(x) for x in numbers_as_str] >> >> That's awfully verbose. A map is simpler: >> >> numbers_as_float = map(float, numbers_as_str) > > I'll pay “verbose”, but not “awfully”. There is little difference in > verbosity between your example and mine. Further, I don't see my example > as excessive, which I assume your “awfully” entails.
Sorry, verbose is not the word I want... I don't know what word I *actually* want, so let me explain. Instead of thinking about a single transformation "change a list of strings to a list of floats", the list comp form forces you to think about the individual list items and the mechanics of looping, and reduces lists to a second-class data type: we can operate on ints without caring about individual bits, but we can't operate on lists without caring about individual list items. Why do I need to care about individual items? The list comp even gives them a name, "x" in your example, even though that name isn't used anywhere else. Why do I need to specify that walking the list must be done from left-to-right rather than whatever order the compiler thinks best, or even in parallel? Answer: I don't, and shouldn't need to. With map, such internal details of how the transformation is performed is hidden. I shouldn't need to specify *how* to convert a list of strings to a list of floats. While a list comp is less verbose than a for-loop, which is less again than a while-loop, they all specify how to do the transformation, which is mental overhead I shouldn't need to care about. Of course, list comps are so seductively easy, and functional programming so conceptually different from what many people are used to, that such over-specification is an awfully easy trap to fall into. I'm sure my own code is filled with similar examples where I use a list comp where a map is more suitable. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
