On Wed, 5 Oct 2011 09:13:20 -0400 Gerald Britton <gerald.britton@gmail.com> wrote:

...

I've received the following comments concerning another>potential use case for PEP 335.>>-------- Original Message -------->Subject: PEP 335 and NumPy NA>Date: Tue, 4 Oct 2011 15:42:50 -0700>From: Mark Wiebe <mwwiebe at gmail.com>>To: Gregory Ewing <greg at cosc.canterbury.ac.nz>>>Hi Greg,>>I took a glance at the python-ideas list, and saw that you're proposing>an update to PEP 335. I recently did a short internship at Enthought>where they asked me to look into the "missing data" problem for NumPy,>and I believe the work from that provides further motivation for the>PEP. Basically, the approach to allow good handling of missing data is>emulating the R programming language by introducing a new value called>NA, similar to the built-in None. For an NA with a boolean type, you get>a three -valued logic, as described>in http://en.wikipedia.org/wiki/Three-valued_logic#Kleene_logic. In the>NA I added to NumPy, this truth table cannot be satisfied because of the>issue PEP 335 add resses:

Interesting! Kinda like SQL, I think, which has True, False and Null (similar to NA in R). Weird to think SQL "solved" this problem 40 years ago!

I wouldn't agree SQL's NULL has solved anything. The rules around NULL calculations are a PITA to use (or work around) and they don't really make sense in any situation I've encountered. Python's None is much saner. I think that, if you want some alternative logic system, you generally use some rule engine of some sort. Mixing two different logics in the same programming language sounds like a recipe for confusion, because the semantics of control flow become context-dependant. Regards Antoine.

On Wed, 5 Oct 2011 09:13:20 -0400 Gerald Britton <gerald.britton@gmail.com> wrote:

...

I've received the following comments concerning another>potential use case for PEP 335.>>-------- Original Message -------->Subject: PEP 335 and NumPy NA>Date: Tue, 4 Oct 2011 15:42:50 -0700>From: Mark Wiebe <mwwiebe at gmail.com>>To: Gregory Ewing <greg at cosc.canterbury.ac.nz>>>Hi Greg,>>I took a glance at the python-ideas list, and saw that you're proposing>an update to PEP 335. I recently did a short internship at Enthought>where they asked me to look into the "missing data" problem for NumPy,>and I believe the work from that provides further motivation for the>PEP. Basically, the approach to allow good handling of missing data is>emulating the R programming language by introducing a new value called>NA, similar to the built-in None. For an NA with a boolean type, you get>a three -valued logic, as described>in http://en.wikipedia.org/wiki/Three-valued_logic#Kleene_logic. In the>NA I added to NumPy, this truth table cannot be satisfied because of the>issue PEP 335 add resses:

Interesting! Kinda like SQL, I think, which has True, False and Null (similar to NA in R). Weird to think SQL "solved" this problem 40 years ago!

I wouldn't agree SQL's NULL has solved anything. The rules around NULL calculations are a PITA to use (or work around) and they don't really make sense in any situation I've encountered. Python's None is much saner. I think that, if you want some alternative logic system, you generally use some rule engine of some sort. Mixing two different logics in the same programming language sounds like a recipe for confusion, because the semantics of control flow become context-dependant. Regards Antoine.