[Python-Dev] Decimal data type issues

[Batista, Facundo]

[Tim Peters]

#- I expect everyone's initial reaction will be to say "no 
#- limit", but think
#- two or three times about that.  Eliminating any restriction 
#- on exponent
#- magnitude is the same as saying overflow can never happen.  
#- But overflow is
#- usually a valuable safety net in real life, telling you that 
#- your algorithm
#- has gone insane.  OTOH, there's nothing with physical 
#- significance that
#- requires an exponent anywhere near as large as 999999999, 
#- and REXX has used
#- that exponent limit for years without problems.

But it's still an artificial restriction. We have no-limit longs, should
have limited Decimal?

And also implies more code and complexity in the module. But this is a side
effect and not the primary concern in the decision.


#- (c) also specifies ways to spell special values, like NaNs 
#- and infinities.
#- Does Decimal(string)?  I don't believe the PEP covered that.

Yes, it does. I missed mention it and an example in the PEP. Already fixed.


#- In any case, from_string() should be subsumed by 
#- Decimal(string), perhaps
#- with via an optional "use_context" flag argument.

You mean something like Decimal(string, use_context=True)? And when creating
from long, for example? Remember that the spec says that the context affect
the operations, not creations (with the exception of from_string).


#- It's quite arguable that str() should be exactly the standard's
#- to_sci_string() (and for those who haven't read the spec, do 
#- before you
#- complain about that -- no, you don't always get an exponent under
#- to_sci_string()).

I'm lost here. Are you saying that str() should have the same behaviour that
to_sci_string()?


#- > Hash behaviour
#- > --------------
#- 
#- Decimals that happen to be exact integers must return the 
#- same hash codes as
#- the hash codes of the ints or longs they're equal to.   All 
#- bets are off wrt
#- hash codes for non-integral Decimals (e.g., 
#- hash(Decimal('1.5')) may or may
#- not be the same as hash(1.5)); promising more than that is simply
#- impractical.
#- 
#- BTW, hash(Decimal('1.0')) must be the same as 
#- hash(Decimal('1.00')) must be
#- the same as hash(Decimal('0.001e3')) despite that they have different
#- internal representations.

I agree completely with this behaviour.


.	Facundo