>>> 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
>>> 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')
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
: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*
: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.
"""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)
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)
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)
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:
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 = []
"""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) + ']')
"""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
"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)
flags=[],
Emax=999999999,
Emin=-999999999,
- capitals=1
+ capitals=1,
+ clamp=0
)
# Pre-made alternate contexts offered by the specification
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
def change_max_exponent(self, exp):
self.context.Emax = exp
def change_clamp(self, clamp):
- self.context._clamp = clamp
+ self.context.clamp = clamp
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))
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.
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