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

Tim Hochberg tim.hochberg at ieee.org
Fri Sep 10 18:33:09 CEST 2004

Greg Ewing wrote:

[SNIP]

Just a couple of quick comments on the motivation:

Motivation ==========

There are many applications in which it is natural to provide custom meanings for Python operators, and in some of these, having boolean operators excluded from those able to be customised can be inconvenient. Examples include: 1. Numeric/Numarray, in which almost all the operators are defined on arrays so as to perform the appropriate operation between corresponding elements, and return an array of the results. For consistency, one would expect a boolean operation between two arrays to return an array of booleans, but this is not currently possible. There is a precedent for an extension of this kind: comparison operators were originally restricted to returning boolean results, and rich comparisons were added so that comparisons of Numeric arrays could return arrays of booleans.

For Numeric/Numarray, I think and1/or1 would be unnecessary. If that were true in general it would simplify the proposal signifigantly: and2/or2 could be renamed to and/or and and1/or1 could be dropped.

2. A symbolic algebra system, in which a Python expression is evaluated in an environment which results in it constructing a tree of objects corresponding to the structure of the expression.

3. A relational database interface, in which a Python expression is used to construct an SQL query.

I would be interested in seeing use cases for either or both of these last two examples that show how and1/or1 are useful.

Regards,

-tim

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