[issue2531] float compared to decimal is silently incorrect.

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

Making float <-> Decimal comparisons return the 'right' answer in 2.x does 
look attractive at first sight, but the more I think about it the more it 
seems a bad idea.  Having the comparisons work in 2.x but not in 3.x seems 
especially nasty, and allowing mixed-type comparisons but not mixed-type 
arithmetic operations also seems somehow unclean.  So -1 from me.  (And 
no, I don't want to add full float <-> Decimal interaction: the Decimal 
module is quite complicated enough as it is.)

Are there many cases where float <-> Decimal comparisons are useful?  The 
only uses I can think of would also involve a need for mixed-type
arithmetic.  In the few cases where it's really needed I don't think it's 
a problem to explicitly convert one or the other type.

The current bogus comparison results also suck, but they're just one 
aspect of a known Python 2.x gotcha.

Would it be possible to raise a warning for Decimal <-> float comparisons?
Does -3 already do this?

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