[Python-Dev] ANN: PEP 335: Overloadable Boolean Operators (original) (raw)

Kevin Jacobs jacobs at theopalgroup.com
Tue Sep 14 17:29:10 CEST 2004

exarkun at divmod.com wrote:

On Tue, 14 Sep 2004 08:04:45 -0400, Kevin Jacobs <jacobs at theopalgroup.com> wrote:

Phillip J. Eby wrote:

For these reasons, I'd feel more comfortable with either a literal syntax (to address algebra, SQL, etc.) or some type of special infix notation to allow new operators to be defined in Python, so that it isn't necessary to use prefix or method notation to perform operations like these. Neither of these solutions burdens applications that don't need the feature(s).

Both of your alternatives are being used in some form and neither is really satisfactory. Literal representations require complex parsers, when the Python parser is really what is desired. Python's parser is already available, through the compiler module. The example given earlier, query("x and y or z"), is relatively straightforward to implement as a set of AST manipulations.

While strictly true, your suggestion still requires two distinct parsers (although one implementation) and two distinct parsing contexts (one embedded in a literal string).

The use cases I care about involve minimizing the difference between evaluating regular Python expressions and ADT instances -- plus the ability to mix constructs from both in a seamless way. If Python didn't support any over-loadable ADT methods, then this wouldn't be an issue. However, the problem is that virtually all ADT methods are defined except logical conjunction and disjunction. Thus, I am more concerned with correcting this oversight than I am with a fraction of a percent in slowdown in real applications. (or at least micro-benchmarks are not representative of any real world situations I've ever cared about)

-Kevin

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