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Type 'g' formatting for Decimal instances doesn't behave in the same way 
as for floats when an explicit precision is given. It should strip all 
trailing zeros from the result:
Python 2.7a0 (trunk:75309, Oct 10 2009, 13:44:18) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from decimal import Decimal
>>> format(Decimal('123.00'), '.6g') # expect '123'
'123.00'
(When no explicit precision is given, Decimal formatting with type 'g' 
tries to preserve the information about the exponent of the Decimal 
instance whenever possible; this also differs from float formatting, but 
it's intentional. This should probably be documented.)