Issue #7279: Make Decimal('nan') hashable. Decimal('snan') remains unhashable.

Also rewrite the Decimal __hash__ method so that it doesn't rely on
float('inf') being valid: float('inf') could raise an exception on
platforms not using IEEE 754 arithmetic.
This commit is contained in:
Mark Dickinson 2010-04-02 10:35:12 +00:00
parent e096e82e82
commit f3eeca16cb
3 changed files with 27 additions and 6 deletions

View file

@ -935,14 +935,30 @@ class Decimal(object):
# The hash of a nonspecial noninteger Decimal must depend only
# on the value of that Decimal, and not on its representation.
# For example: hash(Decimal('100E-1')) == hash(Decimal('10')).
if self._is_special and self._isnan():
raise TypeError('Cannot hash a NaN value.')
# Equality comparisons involving signaling nans can raise an
# exception; since equality checks are implicitly and
# unpredictably used when checking set and dict membership, we
# prevent signaling nans from being used as set elements or
# dict keys by making __hash__ raise an exception.
if self._is_special:
if self.is_snan():
raise TypeError('Cannot hash a signaling NaN value.')
elif self.is_nan():
# 0 to match hash(float('nan'))
return 0
else:
# values chosen to match hash(float('inf')) and
# hash(float('-inf')).
if self._sign:
return -271828
else:
return 314159
# In Python 2.7, we're allowing comparisons (but not
# arithmetic operations) between floats and Decimals; so if
# a Decimal instance is exactly representable as a float then
# its hash should match that of the float. Note that this takes care
# of zeros and infinities, as well as small integers.
# its hash should match that of the float.
self_as_float = float(self)
if Decimal.from_float(self_as_float) == self:
return hash(self_as_float)