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Decimal quantization #494

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Oct 23, 2017
Merged

Decimal quantization #494

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102 changes: 90 additions & 12 deletions babel/numbers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,6 @@
from datetime import date as date_, datetime as datetime_
from itertools import chain
import warnings
from itertools import chain

from babel.core import default_locale, Locale, get_global
from babel._compat import decimal, string_types
Expand Down Expand Up @@ -324,13 +323,27 @@ def format_number(number, locale=LC_NUMERIC):
return format_decimal(number, locale=locale)


def get_decimal_precision(number):
"""Return maximum precision of a decimal instance's fractional part.

Precision is extracted from the fractional part only.
"""
# Copied from: https://github.com/mahmoud/boltons/pull/59
assert isinstance(number, decimal.Decimal)
decimal_tuple = number.normalize().as_tuple()
if decimal_tuple.exponent >= 0:
return 0
return abs(decimal_tuple.exponent)


def get_decimal_quantum(precision):
"""Return minimal quantum of a number, as defined by precision."""
assert isinstance(precision, (int, long, decimal.Decimal))
return decimal.Decimal(10) ** (-precision)


def format_decimal(number, format=None, locale=LC_NUMERIC):
def format_decimal(
number, format=None, locale=LC_NUMERIC, decimal_quantization=True):
u"""Return the given decimal number formatted for a specific locale.

>>> format_decimal(1.2345, locale='en_US')
Expand All @@ -350,23 +363,36 @@ def format_decimal(number, format=None, locale=LC_NUMERIC):
>>> format_decimal(12345.5, locale='en_US')
u'12,345.5'

By default the locale is allowed to truncate and round a high-precision
number by forcing its format pattern onto the decimal part. You can bypass
this behavior with the `decimal_quantization` parameter:

>>> format_decimal(1.2346, locale='en_US')
u'1.235'
>>> format_decimal(1.2346, locale='en_US', decimal_quantization=False)
u'1.2346'

:param number: the number to format
:param format:
:param locale: the `Locale` object or locale identifier
:param decimal_quantization: Truncate and round high-precision numbers to
the format pattern. Defaults to `True`.
"""
locale = Locale.parse(locale)
if not format:
format = locale.decimal_formats.get(format)
pattern = parse_pattern(format)
return pattern.apply(number, locale)
return pattern.apply(
number, locale, decimal_quantization=decimal_quantization)


class UnknownCurrencyFormatError(KeyError):
"""Exception raised when an unknown currency format is requested."""


def format_currency(number, currency, format=None, locale=LC_NUMERIC,
currency_digits=True, format_type='standard'):
def format_currency(
number, currency, format=None, locale=LC_NUMERIC, currency_digits=True,
format_type='standard', decimal_quantization=True):
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Doc for decimal_quantization is missing here too.

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Done in d89365a.

u"""Return formatted currency value.

>>> format_currency(1099.98, 'USD', locale='en_US')
Expand Down Expand Up @@ -416,12 +442,23 @@ def format_currency(number, currency, format=None, locale=LC_NUMERIC,
...
UnknownCurrencyFormatError: "'unknown' is not a known currency format type"

By default the locale is allowed to truncate and round a high-precision
number by forcing its format pattern onto the decimal part. You can bypass
this behavior with the `decimal_quantization` parameter:

>>> format_currency(1099.9876, 'USD', locale='en_US')
u'$1,099.99'
>>> format_currency(1099.9876, 'USD', locale='en_US', decimal_quantization=False)
u'$1,099.9876'

:param number: the number to format
:param currency: the currency code
:param format: the format string to use
:param locale: the `Locale` object or locale identifier
:param currency_digits: use the currency's number of decimal digits
:param currency_digits: use the currency's natural number of decimal digits
:param format_type: the currency format type to use
:param decimal_quantization: Truncate and round high-precision numbers to
the format pattern. Defaults to `True`.
"""
locale = Locale.parse(locale)
if format:
Expand All @@ -434,10 +471,12 @@ def format_currency(number, currency, format=None, locale=LC_NUMERIC,
"%r is not a known currency format type" % format_type)

return pattern.apply(
number, locale, currency=currency, currency_digits=currency_digits)
number, locale, currency=currency, currency_digits=currency_digits,
decimal_quantization=decimal_quantization)


def format_percent(number, format=None, locale=LC_NUMERIC):
def format_percent(
number, format=None, locale=LC_NUMERIC, decimal_quantization=True):
"""Return formatted percent value for a specific locale.

>>> format_percent(0.34, locale='en_US')
Expand All @@ -452,18 +491,31 @@ def format_percent(number, format=None, locale=LC_NUMERIC):
>>> format_percent(25.1234, u'#,##0\u2030', locale='en_US')
u'25,123\u2030'

By default the locale is allowed to truncate and round a high-precision
number by forcing its format pattern onto the decimal part. You can bypass
this behavior with the `decimal_quantization` parameter:

>>> format_percent(23.9876, locale='en_US')
u'2,399%'
>>> format_percent(23.9876, locale='en_US', decimal_quantization=False)
u'2,398.76%'

:param number: the percent number to format
:param format:
:param locale: the `Locale` object or locale identifier
:param decimal_quantization: Truncate and round high-precision numbers to
the format pattern. Defaults to `True`.
"""
locale = Locale.parse(locale)
if not format:
format = locale.percent_formats.get(format)
pattern = parse_pattern(format)
return pattern.apply(number, locale)
return pattern.apply(
number, locale, decimal_quantization=decimal_quantization)


def format_scientific(number, format=None, locale=LC_NUMERIC):
def format_scientific(
number, format=None, locale=LC_NUMERIC, decimal_quantization=True):
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Doc for param missing, same as above

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Done in d89365a.

"""Return value formatted in scientific notation for a specific locale.

>>> format_scientific(10000, locale='en_US')
Expand All @@ -474,15 +526,27 @@ def format_scientific(number, format=None, locale=LC_NUMERIC):
>>> format_scientific(1234567, u'##0.##E00', locale='en_US')
u'1.23E06'

By default the locale is allowed to truncate and round a high-precision
number by forcing its format pattern onto the decimal part. You can bypass
this behavior with the `decimal_quantization` parameter:

>>> format_scientific(1234.9876, u'#.##E0', locale='en_US')
u'1.23E3'
>>> format_scientific(1234.9876, u'#.##E0', locale='en_US', decimal_quantization=False)
u'1.2349876E3'

:param number: the number to format
:param format:
:param locale: the `Locale` object or locale identifier
:param decimal_quantization: Truncate and round high-precision numbers to
the format pattern. Defaults to `True`.
"""
locale = Locale.parse(locale)
if not format:
format = locale.scientific_formats.get(format)
pattern = parse_pattern(format)
return pattern.apply(number, locale)
return pattern.apply(
number, locale, decimal_quantization=decimal_quantization)


class NumberFormatError(ValueError):
Expand Down Expand Up @@ -702,8 +766,13 @@ def scientific_notation_elements(self, value, locale):

return value, exp, exp_sign

def apply(self, value, locale, currency=None, currency_digits=True):
def apply(
self, value, locale, currency=None, currency_digits=True,
decimal_quantization=True):
"""Renders into a string a number following the defined pattern.

Forced decimal quantization is active by default so we'll produce a
number string that is strictly following CLDR pattern definitions.
"""
if not isinstance(value, decimal.Decimal):
value = decimal.Decimal(str(value))
Expand All @@ -724,6 +793,15 @@ def apply(self, value, locale, currency=None, currency_digits=True):
if currency and currency_digits:
frac_prec = (get_currency_precision(currency), ) * 2

# Bump decimal precision to the natural precision of the number if it
# exceeds the one we're about to use. This adaptative precision is only
# triggered if the decimal quantization is disabled or if a scientific
# notation pattern has a missing mandatory fractional part (as in the
# default '#E0' pattern). This special case has been extensively
# discussed at https://github.com/python-babel/babel/pull/494#issuecomment-307649969 .
if not decimal_quantization or (self.exp_prec and frac_prec == (0, 0)):
frac_prec = (frac_prec[0], max([frac_prec[1], get_decimal_precision(value)]))

# Render scientific notation.
if self.exp_prec:
number = ''.join([
Expand Down
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