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#Issue 8540: Make Context._clamp attribute public in decimal module.

This commit is contained in:
Mark Dickinson 2010-05-22 18:35:36 +00:00
parent a92ad7ee2c
commit b1d8e3229c
4 changed files with 88 additions and 20 deletions
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25
Doc/library/decimal.rst
View File

@ -122,7 +122,7 @@ precision, rounding, or enabled traps::
>>> from decimal import *
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999999, Emax=999999999,
capitals=1, flags=[], traps=[Overflow, DivisionByZero,
capitals=1, clamp=0, flags=[], traps=[Overflow, DivisionByZero,
InvalidOperation])
>>> getcontext().prec = 7 # Set a new precision
@ -244,7 +244,7 @@ enabled:
>>> ExtendedContext
Context(prec=9, rounding=ROUND_HALF_EVEN, Emin=-999999999, Emax=999999999,
capitals=1, flags=[], traps=[])
capitals=1, clamp=0, flags=[], traps=[])
>>> setcontext(ExtendedContext)
>>> Decimal(1) / Decimal(7)
Decimal('0.142857143')
@ -269,7 +269,7 @@ using the :meth:`clear_flags` method. ::
Decimal('3.14159292')
>>> getcontext()
Context(prec=9, rounding=ROUND_HALF_EVEN, Emin=-999999999, Emax=999999999,
capitals=1, flags=[Inexact, Rounded], traps=[])
capitals=1, clamp=0, flags=[Inexact, Rounded], traps=[])
The *flags* entry shows that the rational approximation to :const:`Pi` was
rounded (digits beyond the context precision were thrown away) and that the
@ -891,7 +891,7 @@ In addition to the three supplied contexts, new contexts can be created with the
:class:`Context` constructor.
.. class:: Context(prec=None, rounding=None, traps=None, flags=None, Emin=None, Emax=None, capitals=1)
.. class:: Context(prec=None, rounding=None, traps=None, flags=None, Emin=None, Emax=None, capitals=None, clamp=None)
Creates a new context. If a field is not specified or is :const:`None`, the
default values are copied from the :const:`DefaultContext`. If the *flags*
@ -922,6 +922,23 @@ In addition to the three supplied contexts, new contexts can be created with the
:const:`1`, exponents are printed with a capital :const:`E`; otherwise, a
lowercase :const:`e` is used: :const:`Decimal('6.02e+23')`.
The *clamp* field is either :const:`0` (the default) or :const:`1`.
If set to :const:`1`, the exponent ``e`` of a :class:`Decimal`
instance representable in this context is strictly limited to the
range ``Emin - prec + 1 <= e <= Emax - prec + 1``. If *clamp* is
:const:`0` then a weaker condition holds: the adjusted exponent of
the :class:`Decimal` instance is at most ``Emax``. When *clamp* is
:const:`1`, a large normal number will, where possible, have its
exponent reduced and a corresponding number of zeros added to its
coefficient, in order to fit the exponent constraints; this
preserves the value of the number but loses information about
significant trailing zeros. For example::
>>> Context(prec=6, Emax=999, clamp=1).create_decimal('1.23e999')
Decimal('1.23000E+999')
A *clamp* value of :const:`1` allows compatibility with the
fixed-width decimal interchange formats specified in IEEE 754.
The :class:`Context` class defines several general purpose methods as well as
a large number of methods for doing arithmetic directly in a given context.

54
Lib/decimal.py
View File

@ -1611,9 +1611,9 @@ class Decimal(object):
"""Decapitate the payload of a NaN to fit the context"""
payload = self._int
# maximum length of payload is precision if _clamp=0,
# precision-1 if _clamp=1.
max_payload_len = context.prec - context._clamp
# maximum length of payload is precision if clamp=0,
# precision-1 if clamp=1.
max_payload_len = context.prec - context.clamp
if len(payload) > max_payload_len:
payload = payload[len(payload)-max_payload_len:].lstrip('0')
return _dec_from_triple(self._sign, payload, self._exp, True)
@ -1638,11 +1638,11 @@ class Decimal(object):
return Decimal(self)
# if self is zero then exponent should be between Etiny and
# Emax if _clamp==0, and between Etiny and Etop if _clamp==1.
# Emax if clamp==0, and between Etiny and Etop if clamp==1.
Etiny = context.Etiny()
Etop = context.Etop()
if not self:
exp_max = [context.Emax, Etop][context._clamp]
exp_max = [context.Emax, Etop][context.clamp]
new_exp = min(max(self._exp, Etiny), exp_max)
if new_exp != self._exp:
context._raise_error(Clamped)
@ -1702,8 +1702,8 @@ class Decimal(object):
if self_is_subnormal:
context._raise_error(Subnormal)
# fold down if _clamp == 1 and self has too few digits
if context._clamp == 1 and self._exp > Etop:
# fold down if clamp == 1 and self has too few digits
if context.clamp == 1 and self._exp > Etop:
context._raise_error(Clamped)
self_padded = self._int + '0'*(self._exp - Etop)
return _dec_from_triple(self._sign, self_padded, Etop)
@ -2451,7 +2451,7 @@ class Decimal(object):
if not dup:
return _dec_from_triple(dup._sign, '0', 0)
exp_max = [context.Emax, context.Etop()][context._clamp]
exp_max = [context.Emax, context.Etop()][context.clamp]
end = len(dup._int)
exp = dup._exp
while dup._int[end-1] == '0' and exp < exp_max:
@ -3828,13 +3828,13 @@ class Context(object):
Emax - Maximum exponent
capitals - If 1, 1*10^1 is printed as 1E+1.
If 0, printed as 1e1
_clamp - If 1, change exponents if too high (Default 0)
clamp - If 1, change exponents if too high (Default 0)
"""
def __init__(self, prec=None, rounding=None,
traps=None, flags=None,
Emin=None, Emax=None,
capitals=None, _clamp=0,
capitals=None, clamp=None,
_ignored_flags=None):
if flags is None:
flags = []
@ -3855,7 +3855,8 @@ class Context(object):
"""Show the current context."""
s = []
s.append('Context(prec=%(prec)d, rounding=%(rounding)s, '
'Emin=%(Emin)d, Emax=%(Emax)d, capitals=%(capitals)d'
'Emin=%(Emin)d, Emax=%(Emax)d, capitals=%(capitals)d, '
'clamp=%(clamp)d'
% vars(self))
names = [f.__name__ for f, v in self.flags.items() if v]
s.append('flags=[' + ', '.join(names) + ']')
@ -3872,17 +3873,39 @@ class Context(object):
"""Returns a shallow copy from self."""
nc = Context(self.prec, self.rounding, self.traps,
self.flags, self.Emin, self.Emax,
self.capitals, self._clamp, self._ignored_flags)
self.capitals, self.clamp, self._ignored_flags)
return nc
def copy(self):
"""Returns a deep copy from self."""
nc = Context(self.prec, self.rounding, self.traps.copy(),
self.flags.copy(), self.Emin, self.Emax,
self.capitals, self._clamp, self._ignored_flags)
self.capitals, self.clamp, self._ignored_flags)
return nc
__copy__ = copy
# _clamp is provided for backwards compatibility with third-party
# code. May be removed in Python >= 3.3.
def _get_clamp(self):
"_clamp mirrors the clamp attribute. Its use is deprecated."
import warnings
warnings.warn('Use of the _clamp attribute is deprecated. '
'Please use clamp instead.',
DeprecationWarning)
return self.clamp
def _set_clamp(self, clamp):
"_clamp mirrors the clamp attribute. Its use is deprecated."
import warnings
warnings.warn('Use of the _clamp attribute is deprecated. '
'Please use clamp instead.',
DeprecationWarning)
self.clamp = clamp
# don't bother with _del_clamp; no sane 3rd party code should
# be deleting the _clamp attribute
_clamp = property(_get_clamp, _set_clamp)
def _raise_error(self, condition, explanation = None, *args):
"""Handles an error
@ -3965,7 +3988,7 @@ class Context(object):
"permitted.")
d = Decimal(num, context=self)
if d._isnan() and len(d._int) > self.prec - self._clamp:
if d._isnan() and len(d._int) > self.prec - self.clamp:
return self._raise_error(ConversionSyntax,
"diagnostic info too long in NaN")
return d._fix(self)
@ -5875,7 +5898,8 @@ DefaultContext = Context(
flags=[],
Emax=999999999,
Emin=-999999999,
capitals=1
capitals=1,
clamp=0
)
# Pre-made alternate contexts offered by the specification

24
Lib/test/test_decimal.py
View File

@ -27,11 +27,13 @@ with the corresponding argument.
import math
import os, sys
import operator
import warnings
import pickle, copy
import unittest
from decimal import *
import numbers
from test.support import run_unittest, run_doctest, is_resource_enabled
from test.support import check_warnings
import random
try:
import threading
@ -412,7 +414,7 @@ class DecimalTest(unittest.TestCase):
def change_max_exponent(self, exp):
self.context.Emax = exp
def change_clamp(self, clamp):
self.context._clamp = clamp
self.context.clamp = clamp
@ -1815,6 +1817,26 @@ class ContextAPItests(unittest.TestCase):
self.assertNotEqual(id(c.flags), id(d.flags))
self.assertNotEqual(id(c.traps), id(d.traps))
def test__clamp(self):
# In Python 3.2, the private attribute `_clamp` was made
# public (issue 8540), with the old `_clamp` becoming a
# property wrapping `clamp`. For the duration of Python 3.2
# only, the attribute should be gettable/settable via both
# `clamp` and `_clamp`; in Python 3.3, `_clamp` should be
# removed.
c = Context(clamp = 0)
self.assertEqual(c.clamp, 0)
with check_warnings(("", DeprecationWarning)):
c._clamp = 1
self.assertEqual(c.clamp, 1)
with check_warnings(("", DeprecationWarning)):
self.assertEqual(c._clamp, 1)
c.clamp = 0
self.assertEqual(c.clamp, 0)
with check_warnings(("", DeprecationWarning)):
self.assertEqual(c._clamp, 0)
def test_abs(self):
c = Context()
d = c.abs(Decimal(-1))

5
Misc/NEWS
View File

@ -393,6 +393,11 @@ C-API
Library
-------
- Issue #8540: Decimal module: rename the Context._clamp attribute to
Context.clamp and make it public. This is useful in creating
contexts that correspond to the decimal interchange formats
specified in IEEE 754.
- Issue #6268: Fix seek() method of codecs.open(), don't read or write the BOM
twice after seek(0). Fix also reset() method of codecs, UTF-16, UTF-32 and
StreamWriter classes.