Bugs item #1770416, was opened at 2007-08-08 18:13
Message generated for change (Comment added) made by aryx
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Jason G (aryx)
Assigned to: Nobody/Anonymous (nobody)
Summary: Decimal.__int__ overflows for large values
Initial Comment:
This also affects Decimal.__hash__, since it [indirectly] calls Decimal.__int__.
>>> from decimal import Decimal as D
>>> e = D("1e1234567890987654321")
>>> int(e)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.5/decimal.py", line 1501, in __int__
s = ''.join(map(str, self._int)) + '0'*self._exp
OverflowError: cannot fit 'long' into an index-sized integer
>>> e = D("1e1234567890")
>>> int(e)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.5/decimal.py", line 1501, in __int__
s = ''.join(map(str, self._int)) + '0'*self._exp
MemoryError
Also, for values that do work this is incredibly slow if they are still fairly
large.
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>Comment By: Jason G (aryx)
Date: 2007-08-09 12:39
Message:
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Hey Daniel,
The bigger issue for us is mostly the fact that Decimal.__hash__ us
calling Decimal.__int__ and not because we want an integer/long version of
a very large Decimal. We do not actually cast the decimal into an int/long
explicitly. I wouldn't have any issues if Decimal.__int__ remained as it
is, but I think it would be a good idea for Decimal.__hash__ to do
something differently. Probably something that is fast and simple, such as
hash( self.as_tuple() ), self being a Decimal of course.
Our project is a CAS and we use Decimal for our real number class. I
happened to run into this issue when I was implementing approximation of
log(x) for extremely large/small values of x. I just started keyboard
bashing numbers and behold, Decimal crashed on me :)
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Comment By: ajaksu (ajaksu2)
Date: 2007-08-09 05:39
Message:
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Hi Jason,
The OverflowError is related to "index-sized ints" as in "ints that are
valid indexes for sequences", try:
>>> e = "0" * 1234567890
So it seems that this error is avoiding the creation of a string of length
1234567890, which is a good thing (sorta) :)
Once I tried to implement a dec2long function that was based on numbers
instead of strings, see if it helps (it's VERY slow and naive, but IIRC it
was a bit faster than the original version and correct):
http://groups.google.com/group/comp.lang.python/msg/aba7264ab38eb25e
Now, do you really need all that precision for such huge numbers? I know I
didn't ;)
Daniel
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