Implementing long division using a generator function in python

问题

As an exercise to try to understand generator functions I am trying to write a function that simulates long division and returns the number one digit at a time. I have written this function and it doesn't seem to work. However if I step through it line by line in the shell it does exactly what I want it to do so I'm not sure what to do going forward. I've read through posts on the internet about generator functions here:

and from what I understand I just replace the return statement with a yield statement. Is this not the case? Can anybody please tell me what I am doing wrong? Any help is appreciated.

def decimals(number):    
    """
    Takes a numnber and generates the digits of  1/n.

    """
    divisor = number
    dividend = 1


    while dividend % divisor != 0:
        #Floor division is the // operator        
        quotient = divisor // dividend
        remainder = dividend % divisor

        temp = quotient * divisor
        if remainder != 0 :
            temp = quotient * divisor

        if temp > dividend:
            dividend = dividend * 10
            dividend = dividend - temp
        else:
            dividend = dividend - temp
        yield quotient



def main():
    gen = decimals(4)
    print(next(gen))

if __name__ == "__main__":
    main()

回答1:

Your main problem is that you output only a single value from the generator: next(gen). To output the whole generator, make a list from it's values: print(list(decimals(4))), or print it value by value:

for digit in decimals(4):
    print(digit)

To deal with endless generators (e.g., from a decimals(3) call), you can for example take only a limited amount of values from it with itertools.islice:

from itertools import islice
for digit in islice(decimals(3), 10):
    print(digit)

Also, I think there is something wrong with your algorithm. It doesn't seem to produce the correct results. I think, it should look something like this:

def decimals(number):    
    """
    Takes a number and generates the digits of  1/n.

    """
    divisor = number
    dividend = 1
    remainder = 1

    while remainder:
        #Floor division is the // operator        
        quotient = dividend // divisor
        remainder = dividend % divisor

        if remainder < divisor:
            dividend = remainder * 10
        else:
            dividend = remainder
        yield quotient

As a side note, this code may still be made shorter. For example:

def decimals(number):    
    dividend = 1
    while dividend:      
        yield dividend // number
        dividend = dividend % number * 10

来源：https://stackoverflow.com/questions/29424349/implementing-long-division-using-a-generator-function-in-python

标签

python

python-2.7

generator

division