[Python-Dev] decimal.py signals & traps (original) (raw)

Raymond Hettinger python at rcn.com
Thu Jul 8 13:38:54 CEST 2004

[David Goodger]

Please take a look at the patch I submitted to SourceForge: <http://python.org/sf/987300>. decimal.Signals is changed to list signals, not conditions. Context.raiseerror is modified to handle signals properly.

This should be tackled in steps and as part of larger improvement to the context API.

The most uncomfortable part of the Python interface to contexts is creating the dictionaries for traps and flags arguments. Besides being a pain to create and display, there are issues with two contexts sharing the same underlying dictionaries. Also, it makes it difficult to address the issue at hand (as noted by the one XXX comment in the module and by your bug report).

As a first step, I would like change the Context constructor API to match the format in Context.repr. That format is somewhat easier to use and less verbose (list only the flags and traps that you want set). Also, I would add accessor methods patterned after the Language Independent Arithmetic standard (LIA-1) to set, clear, and test flags and traps. The dictionaries themselves would be made private (allowing them to be recast as sets if desired).

With a method interface in place, a next step would be to add logic to maintain relationships between signals. Setting the ConversionSyntax flag also sets the InvalidOperation flag. Likewise setting a trap for InvalidOperation would set the trap for ConversionSyntax.

As a side benefit, the above changes will make it easier to someday implement the module in C. Holding user supplied, volatile dictionaries was not a recipe for success in that regard.

I'm less enthusiastic about changing any of the exception names but none of the above precludes that as a last step.

Raymond

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