Can we stop this thread now? :) I think we've all seen what the intended behavior of sum(), max() and other similar functions.
cheers James On Mon, Sep 8, 2008 at 3:30 AM, Mensanator <[EMAIL PROTECTED]> wrote: > On Sep 6, 11:05�pm, Steven D'Aprano <[EMAIL PROTECTED] > cybersource.com.au> wrote: >> On Sat, 06 Sep 2008 11:22:07 -0700, Mensanator wrote: >> >> [...] >> >> >> They could have decided that sum must take at least two arguments, >> >> because addition requires two arguments and it's meaningless to talk >> >> about adding a single number without talking about adding it to >> >> something else. But they didn't. >> >> > Ok. But the problem is they DID in SQL: x + Null = Null. >> >> Sheesh. That's not a problem, because Python is not trying to be a >> dialect of SQL. > > And yet, they added a Sqlite3 module. > >> >> If you want a NULL object, then there are recipes on the web that will >> give you one. Then all you need to do is call sum(alist or [NULL]) and it >> will give you the behaviour you want. > > Actualy, I already get the behaviour I want. sum([1,None]) > throws an exception. I don't see why sum([]) doesn't throw > an exception also (I understand that behaviour is by design, > I'm merely pointing out that the design doesn't cover every > situation). > >> >> [...] >> >> > Here's a real world example (no ivory tower stuff): >> >> > An oil refinery client has just excavated a big pile of dirt to lay a >> > new pipeline. >> [snip details] >> > Can't I just use a sum of 0 to tell me when data is missing? No, because >> > in some cases the reporting limit of undetected compounds is set to 0. >> >> You can't use a sum of 0 to indicate when data is missing, full stop. > > Exactly. That's why I would prefer sum([]) to raise an > exception instead of giving a false positive. > >> The >> data may require 15 tests when only 3 have actually been done: >> >> sum([1.2e-7, 9.34e-6, 2.06e-8]) > > Biggest problem here is that it is often unknown just > how many records you're supposed to get from the query, > so we can't tell that a count of 3 is supposed to be 15. > >> >> Missing data and a non-zero sum. How should sum() deal with that? > > That's a seperate issue and I'm not saying it should as > long as the list contains actual numbers to sum. > sum([1.2e-7, 9.34e-6, 2.06e-8, None]) will raise an > exception, as it should. But what types are contained > in []? > >> >> The answer is that sum() can't deal with that. You can't expect sum() to >> read your mind, know that there should be 15 items instead of 3, and >> raise an error. So why do you expect sum() to read your mind and >> magically know that zero items is an error, especially when for many >> applications it is NOT an error? > > For the simple reason it doesn't have to read your mind, > a mechanism has already been built into the function: start > value. For those situations where an empty list is desired > to sum to 0, you could use sum(alist,0) and use sum(alist) for > those cases where summing an empty list is meaningless. > Shouldn't you have to explicitly tell sum() how deal with > situations like empty lists rather than have it implicitly > assume a starting value of 0 when you didn't ask for it? > >> >> The behaviour you want for this specific application is unwanted, >> unnecessary and even undesirable for many other applications. The >> solution is for *you* to write application-specific code to do what your >> application needs, instead of relying on a general purpose function >> magically knowing what you want. > > Does division magically know what you want? No, it raises an > exception when you do something like divide by 0. Isn't it > Pythonic to not write a litany of tests to cover every > possible case, but instead use try:except? > > But try:except only works if the errors are recognized. > And sum() says that summing an empty list is NEVER an error > under ANY circumstance. That may be true in MOST cases, but > it certainly isn't true in ALL cases. > >> >> -- >> Steven > > -- > http://mail.python.org/mailman/listinfo/python-list -- -- -- "Problems are solved by method" -- http://mail.python.org/mailman/listinfo/python-list
