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Make rational.gcd() public and allow Rational to take decimal strings, per

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Raymond's advice.
This commit is contained in:
Jeffrey Yasskin 2008-01-27 05:40:35 +00:00
parent 46c61b2c1d
commit 3e1a373616
2 changed files with 62 additions and 21 deletions
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37
Lib/rational.py
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@ -14,8 +14,8 @@ __all__ = ["Rational"]
RationalAbc = numbers.Rational
def _gcd(a, b): # XXX This is a useful function. Consider making it public.
"""Calculate the Greatest Common Divisor.
def gcd(a, b):
"""Calculate the Greatest Common Divisor of a and b.
Unless b==0, the result will have the same sign as b (so that when
b is divided by it, the result comes out positive).
@ -40,8 +40,8 @@ def _binary_float_to_ratio(x):
>>> _binary_float_to_ratio(-.25)
(-1, 4)
"""
# XXX Consider moving this to to floatobject.c
# with a name like float.as_intger_ratio()
# XXX Move this to floatobject.c with a name like
# float.as_integer_ratio()
if x == 0:
return 0, 1
@ -80,12 +80,9 @@ def _binary_float_to_ratio(x):
_RATIONAL_FORMAT = re.compile(
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)(?:/(?P<denom>\d+))?\s*$')
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)'
r'(?:/(?P<denom>\d+)|\.(?P<decimal>\d+))?\s*$')
# XXX Consider accepting decimal strings as input since they are exact.
# Rational("2.01") --> s="2.01" ; Rational.from_decimal(Decimal(s)) --> Rational(201, 100)"
# If you want to avoid going through the decimal module, just parse the string directly:
# s.partition('.') --> ('2', '.', '01') --> Rational(int('2'+'01'), 10**len('01')) --> Rational(201, 100)
class Rational(RationalAbc):
"""This class implements rational numbers.
@ -96,7 +93,7 @@ class Rational(RationalAbc):
Rational() == 0.
Rationals can also be constructed from strings of the form
'[-+]?[0-9]+(/[0-9]+)?', optionally surrounded by spaces.
'[-+]?[0-9]+((/|.)[0-9]+)?', optionally surrounded by spaces.
"""
@ -106,7 +103,8 @@ class Rational(RationalAbc):
def __new__(cls, numerator=0, denominator=1):
"""Constructs a Rational.
Takes a string, another Rational, or a numerator/denominator pair.
Takes a string like '3/2' or '3.2', another Rational, or a
numerator/denominator pair.
"""
self = super(Rational, cls).__new__(cls)
@ -118,9 +116,18 @@ class Rational(RationalAbc):
m = _RATIONAL_FORMAT.match(input)
if m is None:
raise ValueError('Invalid literal for Rational: ' + input)
numerator = int(m.group('num'))
# Default denominator to 1. That's the only optional group.
denominator = int(m.group('denom') or 1)
numerator = m.group('num')
decimal = m.group('decimal')
if decimal:
# The literal is a decimal number.
numerator = int(numerator + decimal)
denominator = 10**len(decimal)
else:
# The literal is an integer or fraction.
numerator = int(numerator)
# Default denominator to 1.
denominator = int(m.group('denom') or 1)
if m.group('sign') == '-':
numerator = -numerator
@ -139,7 +146,7 @@ class Rational(RationalAbc):
if denominator == 0:
raise ZeroDivisionError('Rational(%s, 0)' % numerator)
g = _gcd(numerator, denominator)
g = gcd(numerator, denominator)
self.numerator = int(numerator // g)
self.denominator = int(denominator // g)
return self