Folks: I've uploaded a small package to PyPI which is a small wrapper around simplejson that sets the default behavior so that JSON decimal values are mapped to type Decimal instead of type float:
http://pypi.python.org/pypi/jsonutil It has pretty thorough unit tests, including a copy of all the simplejson unit tests, which I copied into the jsonutil package, as well as a few added tests to test the new functionality. I also did some benchmarks to satisfy myself that using jsonutil isn't noticeably slower than using simplejson. You can find the benchmarking code in the package, but I'm not sure if it comes with documentation sufficient to let you easily run the benchmarks yourself. I did this originally on behalf of my employer, SimpleGeo, who now use this wrapper in our production system. Based on my reasoning and also SimpleGeo's experience, this introduced absolutely no compatibility problems between our service (an HTTP API) and users of our service, who themselves parse and construct JSON however they want (typically from other languages like Ruby and PHP). This is because no user of our API sends a string like "0.03" and then expects to get back "0.029999999999999999" and breaks in some way if we instead send back "0.03". If there were clients like that, then they would have broken when we made this change, because formerly, using simplejson, we would have accepted "0.03" and then sent back "0.029999999999999999", but now, using jsonutil, we accept "0.03" and send back "0.03". I would expect clients that breaks in such a case to be rare, but of course computer systems are always surprising me with their creative ways to be fragile and failure-prone, so I wouldn't bet against a few such systems existing. If anyone spots one in the wild, please let me know. Converting from simplejson (default float) to jsonutil (default Decimal) did, as expected, cause type mismatches internally inside our server, where some calling code was expecting float and the called code was returning Decimal, or vice versa. So far these problems were all "shallow" in that they could be fixed by adding a cast or by changing one side or the other, as desired. In short, I advise people not to fear using Python Decimals to manage their JSON decimal strings. It will probably introduce zero incompatibilities across the wire, and any type mismatches it introduces within your own code base will probably be easy to fix. Regards, Zooko -- http://mail.python.org/mailman/listinfo/python-list
