python class fraction numbers

问题:

I made a code that makes the user input two fraction numbers in the form "d/n".

How can I make it print the reduced form of the fraction ?

ex: when I type 2/4 it prints 1/2?

   import sys

class Rational:

  def __init__(self,n,d):
    self.numerator= n
    self.denominator= d
  def value(self):
    return float(self.numerator)/float(self.denominator)

  def __repr__(self):
    return "%d/%d ~ %g" % (self.numerator,self.denominator,self.value())
  def read(self):
    while 1:
      try:
        s=raw_input("Enter fraction n/d: ")
        n,d= s.split("/")
        self.numerator= int(n)
        self.denominator= int(d)
      except KeyboardInterrupt:
        print
        exit()
      except:
        print sys.exc_info()[0]
        print "bad input, try again."
      else:
        if int(d)==0:
          print "The denominator cannot be zero. Try again."
        elif int(d)<0:
          print "The denominator cannot be negative. Try again."
        else:
          return

r1=Rational(1,1)
r1.read()
print r1

r2=Rational(1,1)
r2.read()
print r2

回答1:

Use the fractions.Fraction() class and have it do the work for you:

>>> import fractions
>>> fractions.Fraction(2, 4)
Fraction(1, 2)

To simplify fractions yourself, calculate the greatest common divisor:

def gcd(a, b):
    while b:
        a, b = b, a%b
    return a

g = gcd(numerator, denominator)
numerator //= g
denominator //= g

回答2:

    >>> num = 2
    >>> den = 4        
    >>> from fractions import Fraction
    >>> frac = Fraction(num,den).limit_denominator()
    >>> numer = frac.numerator
    >>> denom = frac.denominator
    >>> print '%d/%d ~ %g' % (numer, denom, float(numer)/denom)
    1/2 ~ 0.5

Hope this helps. (link http://docs.python.org/2/library/fractions.html)

回答3:

Simply divide the numerator and the denominator to their greatest common divisor before showing the number. That is if you want to use your own class. Otherwise there is a Fraction class in the fractions module.

回答4:

Well, first you're going to have to add support to your Rational class that computes the reduced form for a fraction. Basically, what you need to do is add a reduce() method that finds the lowest common denominator of the two numerator, denominator in the Rational. Try looking at Least Common Multiple for an algorithm.

回答5:

import fractions

f = fractions.Fraction(5, 10)
print (f) # print 1/2