Hmm. I'm not sure that it ever got documented properly. There may still be an open documentation issue somewhere.

There's not really much wiggle-room for changing the implementation: the behaviour of the "g" formatting for Decimal objects is following the specification of "to-scientific-string" from the Decimal Arithmetic spec that the decimal module is based on: http://speleotrove.com/decimal/daconvs.html#reftostr

One of the principles articulated there is that to-scientific-string should be faithful, so that conversion to string and back doesn't lose any information. That precludes chopping significant trailing zeros.