mirror of https://github.com/python/cpython
Add __format__ method to Decimal, to support PEP 3101
This commit is contained in:
Mark Dickinson
parent
b4cbc98c39
commit
1ddf1d8482
240
Lib/decimal.py
240
Lib/decimal.py
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@ -2380,6 +2380,29 @@ class Decimal(object):
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coeff = str(int(coeff)+1)
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return _dec_from_triple(self._sign, coeff, exp)
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def _round(self, places, rounding):
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"""Round a nonzero, nonspecial Decimal to a fixed number of
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significant figures, using the given rounding mode.
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Infinities, NaNs and zeros are returned unaltered.
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This operation is quiet: it raises no flags, and uses no
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information from the context.
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"""
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if places <= 0:
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raise ValueError("argument should be at least 1 in _round")
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if self._is_special or not self:
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return Decimal(self)
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ans = self._rescale(self.adjusted()+1-places, rounding)
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# it can happen that the rescale alters the adjusted exponent;
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# for example when rounding 99.97 to 3 significant figures.
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# When this happens we end up with an extra 0 at the end of
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# the number; a second rescale fixes this.
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if ans.adjusted() != self.adjusted():
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ans = ans._rescale(ans.adjusted()+1-places, rounding)
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return ans
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def to_integral_exact(self, rounding=None, context=None):
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"""Rounds to a nearby integer.
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@ -3431,6 +3454,95 @@ class Decimal(object):
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return self # My components are also immutable
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return self.__class__(str(self))
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# PEP 3101 support. See also _parse_format_specifier and _format_align
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def __format__(self, specifier, context=None):
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"""Format a Decimal class according to the given specifier.
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The specifier should be a standard format specifier, with the
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form described in PEP 3101. Formatting types 'e', 'E', 'f',
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'F', 'g', 'G', and '%' are supported. If the formatting type
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is omitted it defaults to 'g' or 'G', depending on the value
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of context.capitals.
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At this time the 'n' format specifier type (which is supposed
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to use the current locale) is not supported.
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"""
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# Note: PEP 3101 says that if the type is not present then
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# there should be at least one digit after the decimal point.
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# We take the liberty of ignoring this requirement for
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# Decimal---it's presumably there to make sure that
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# format(float, '') behaves similarly to str(float).
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if context is None:
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context = getcontext()
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spec = _parse_format_specifier(specifier)
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# special values don't care about the type or precision...
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if self._is_special:
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return _format_align(str(self), spec)
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# a type of None defaults to 'g' or 'G', depending on context
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# if type is '%', adjust exponent of self accordingly
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if spec['type'] is None:
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spec['type'] = ['g', 'G'][context.capitals]
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elif spec['type'] == '%':
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self = _dec_from_triple(self._sign, self._int, self._exp+2)
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# round if necessary, taking rounding mode from the context
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rounding = context.rounding
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precision = spec['precision']
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if precision is not None:
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if spec['type'] in 'eE':
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self = self._round(precision+1, rounding)
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elif spec['type'] in 'gG':
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if len(self._int) > precision:
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self = self._round(precision, rounding)
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elif spec['type'] in 'fF%':
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self = self._rescale(-precision, rounding)
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# special case: zeros with a positive exponent can't be
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# represented in fixed point; rescale them to 0e0.
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elif not self and self._exp > 0 and spec['type'] in 'fF%':
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self = self._rescale(0, rounding)
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# figure out placement of the decimal point
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leftdigits = self._exp + len(self._int)
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if spec['type'] in 'fF%':
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dotplace = leftdigits
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elif spec['type'] in 'eE':
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if not self and precision is not None:
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dotplace = 1 - precision
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else:
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dotplace = 1
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elif spec['type'] in 'gG':
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if self._exp <= 0 and leftdigits > -6:
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dotplace = leftdigits
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else:
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dotplace = 1
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# figure out main part of numeric string...
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if dotplace <= 0:
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num = '0.' + '0'*(-dotplace) + self._int
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elif dotplace >= len(self._int):
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# make sure we're not padding a '0' with extra zeros on the right
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assert dotplace==len(self._int) or self._int != '0'
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num = self._int + '0'*(dotplace-len(self._int))
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else:
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num = self._int[:dotplace] + '.' + self._int[dotplace:]
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# ...then the trailing exponent, or trailing '%'
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if leftdigits != dotplace or spec['type'] in 'eE':
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echar = {'E': 'E', 'e': 'e', 'G': 'E', 'g': 'e'}[spec['type']]
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num = num + "{0}{1:+}".format(echar, leftdigits-dotplace)
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elif spec['type'] == '%':
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num = num + '%'
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# add sign
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if self._sign == 1:
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num = '-' + num
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return _format_align(num, spec)
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def _dec_from_triple(sign, coefficient, exponent, special=False):
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"""Create a decimal instance directly, without any validation,
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normalization (e.g. removal of leading zeros) or argument
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@ -5250,8 +5362,136 @@ _parser = re.compile(r""" # A numeric string consists of:
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_all_zeros = re.compile('0*$').match
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_exact_half = re.compile('50*$').match
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##### PEP3101 support functions ##############################################
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# The functions parse_format_specifier and format_align have little to do
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# with the Decimal class, and could potentially be reused for other pure
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# Python numeric classes that want to implement __format__
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#
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# A format specifier for Decimal looks like:
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#
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# [[fill]align][sign][0][minimumwidth][.precision][type]
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#
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_parse_format_specifier_regex = re.compile(r"""\A
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(?:
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(?P<fill>.)?
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(?P<align>[<>=^])
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)?
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(?P<sign>[-+ ])?
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(?P<zeropad>0)?
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(?P<minimumwidth>(?!0)\d+)?
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(?:\.(?P<precision>0|(?!0)\d+))?
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(?P<type>[eEfFgG%])?
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\Z
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""", re.VERBOSE)
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del re
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def _parse_format_specifier(format_spec):
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"""Parse and validate a format specifier.
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Turns a standard numeric format specifier into a dict, with the
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following entries:
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fill: fill character to pad field to minimum width
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align: alignment type, either '<', '>', '=' or '^'
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sign: either '+', '-' or ' '
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minimumwidth: nonnegative integer giving minimum width
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precision: nonnegative integer giving precision, or None
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type: one of the characters 'eEfFgG%', or None
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unicode: either True or False (always True for Python 3.x)
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"""
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m = _parse_format_specifier_regex.match(format_spec)
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if m is None:
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raise ValueError("Invalid format specifier: " + format_spec)
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# get the dictionary
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format_dict = m.groupdict()
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# defaults for fill and alignment
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fill = format_dict['fill']
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align = format_dict['align']
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if format_dict.pop('zeropad') is not None:
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# in the face of conflict, refuse the temptation to guess
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if fill is not None and fill != '0':
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raise ValueError("Fill character conflicts with '0'"
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" in format specifier: " + format_spec)
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if align is not None and align != '=':
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raise ValueError("Alignment conflicts with '0' in "
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"format specifier: " + format_spec)
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fill = '0'
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align = '='
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format_dict['fill'] = fill or ' '
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format_dict['align'] = align or '<'
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if format_dict['sign'] is None:
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format_dict['sign'] = '-'
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# turn minimumwidth and precision entries into integers.
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# minimumwidth defaults to 0; precision remains None if not given
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format_dict['minimumwidth'] = int(format_dict['minimumwidth'] or '0')
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if format_dict['precision'] is not None:
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format_dict['precision'] = int(format_dict['precision'])
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# if format type is 'g' or 'G' then a precision of 0 makes little
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# sense; convert it to 1. Same if format type is unspecified.
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if format_dict['precision'] == 0:
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if format_dict['type'] in 'gG' or format_dict['type'] is None:
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format_dict['precision'] = 1
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# record whether return type should be str or unicode
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format_dict['unicode'] = isinstance(format_spec, unicode)
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return format_dict
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def _format_align(body, spec_dict):
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"""Given an unpadded, non-aligned numeric string, add padding and
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aligment to conform with the given format specifier dictionary (as
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output from parse_format_specifier).
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It's assumed that if body is negative then it starts with '-'.
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Any leading sign ('-' or '+') is stripped from the body before
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applying the alignment and padding rules, and replaced in the
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appropriate position.
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"""
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# figure out the sign; we only examine the first character, so if
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# body has leading whitespace the results may be surprising.
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if len(body) > 0 and body[0] in '-+':
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sign = body[0]
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body = body[1:]
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else:
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sign = ''
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if sign != '-':
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if spec_dict['sign'] in ' +':
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sign = spec_dict['sign']
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else:
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sign = ''
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# how much extra space do we have to play with?
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minimumwidth = spec_dict['minimumwidth']
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fill = spec_dict['fill']
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padding = fill*(max(minimumwidth - (len(sign+body)), 0))
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align = spec_dict['align']
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if align == '<':
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result = padding + sign + body
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elif align == '>':
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result = sign + body + padding
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elif align == '=':
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result = sign + padding + body
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else: #align == '^'
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half = len(padding)//2
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result = padding[:half] + sign + body + padding[half:]
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# make sure that result is unicode if necessary
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if spec_dict['unicode']:
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result = unicode(result)
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return result
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##### Useful Constants (internal use only) ################################
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@ -615,6 +615,98 @@ class DecimalImplicitConstructionTest(unittest.TestCase):
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self.assertEqual(eval('Decimal(10)' + sym + 'E()'),
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'10' + rop + 'str')
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class DecimalFormatTest(unittest.TestCase):
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'''Unit tests for the format function.'''
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def test_formatting(self):
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# triples giving a format, a Decimal, and the expected result
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test_values = [
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('e', '0E-15', '0e-15'),
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('e', '2.3E-15', '2.3e-15'),
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('e', '2.30E+2', '2.30e+2'), # preserve significant zeros
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('e', '2.30000E-15', '2.30000e-15'),
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('e', '1.23456789123456789e40', '1.23456789123456789e+40'),
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('e', '1.5', '1.5e+0'),
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('e', '0.15', '1.5e-1'),
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('e', '0.015', '1.5e-2'),
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('e', '0.0000000000015', '1.5e-12'),
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('e', '15.0', '1.50e+1'),
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('e', '-15', '-1.5e+1'),
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('e', '0', '0e+0'),
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('e', '0E1', '0e+1'),
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('e', '0.0', '0e-1'),
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('e', '0.00', '0e-2'),
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('.6e', '0E-15', '0.000000e-9'),
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('.6e', '0', '0.000000e+6'),
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('.6e', '9.999999', '9.999999e+0'),
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('.6e', '9.9999999', '1.000000e+1'),
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('.6e', '-1.23e5', '-1.230000e+5'),
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('.6e', '1.23456789e-3', '1.234568e-3'),
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('f', '0', '0'),
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('f', '0.0', '0.0'),
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('f', '0E-2', '0.00'),
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('f', '0.00E-8', '0.0000000000'),
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('f', '0E1', '0'), # loses exponent information
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('f', '3.2E1', '32'),
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('f', '3.2E2', '320'),
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('f', '3.20E2', '320'),
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('f', '3.200E2', '320.0'),
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('f', '3.2E-6', '0.0000032'),
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('.6f', '0E-15', '0.000000'), # all zeros treated equally
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('.6f', '0E1', '0.000000'),
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('.6f', '0', '0.000000'),
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('.0f', '0', '0'), # no decimal point
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('.0f', '0e-2', '0'),
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('.0f', '3.14159265', '3'),
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('.1f', '3.14159265', '3.1'),
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('.4f', '3.14159265', '3.1416'),
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('.6f', '3.14159265', '3.141593'),
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('.7f', '3.14159265', '3.1415926'), # round-half-even!
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('.8f', '3.14159265', '3.14159265'),
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('.9f', '3.14159265', '3.141592650'),
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('g', '0', '0'),
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('g', '0.0', '0.0'),
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('g', '0E1', '0e+1'),
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('G', '0E1', '0E+1'),
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('g', '0E-5', '0.00000'),
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('g', '0E-6', '0.000000'),
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('g', '0E-7', '0e-7'),
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('g', '-0E2', '-0e+2'),
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('.0g', '3.14159265', '3'), # 0 sig fig -> 1 sig fig
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('.1g', '3.14159265', '3'),
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('.2g', '3.14159265', '3.1'),
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('.5g', '3.14159265', '3.1416'),
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('.7g', '3.14159265', '3.141593'),
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('.8g', '3.14159265', '3.1415926'), # round-half-even!
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('.9g', '3.14159265', '3.14159265'),
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('.10g', '3.14159265', '3.14159265'), # don't pad
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('%', '0E1', '0%'),
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('%', '0E0', '0%'),
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('%', '0E-1', '0%'),
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('%', '0E-2', '0%'),
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('%', '0E-3', '0.0%'),
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('%', '0E-4', '0.00%'),
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('.3%', '0', '0.000%'), # all zeros treated equally
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('.3%', '0E10', '0.000%'),
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('.3%', '0E-10', '0.000%'),
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('.3%', '2.34', '234.000%'),
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('.3%', '1.234567', '123.457%'),
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('.0%', '1.23', '123%'),
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('e', 'NaN', 'NaN'),
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('f', '-NaN123', '-NaN123'),
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('+g', 'NaN456', '+NaN456'),
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('.3e', 'Inf', 'Infinity'),
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('.16f', '-Inf', '-Infinity'),
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('.0g', '-sNaN', '-sNaN'),
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('', '1.00', '1.00'),
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]
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for fmt, d, result in test_values:
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self.assertEqual(format(Decimal(d), fmt), result)
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class DecimalArithmeticOperatorsTest(unittest.TestCase):
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'''Unit tests for all arithmetic operators, binary and unary.'''
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@ -1363,6 +1455,7 @@ def test_main(arith=False, verbose=None, todo_tests=None, debug=None):
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DecimalExplicitConstructionTest,
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DecimalImplicitConstructionTest,
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DecimalArithmeticOperatorsTest,
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DecimalFormatTest,
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DecimalUseOfContextTest,
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DecimalUsabilityTest,
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DecimalPythonAPItests,
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