Convert fraction to string with repeating decimal places in brackets

Question

I want to write a function in Python 3 that converts fractions given as numerator and denominator into their string representation as decimal number, but with repeating decimal places in brackets.

An example:

• convert(1, 4) should output "0.25"
• convert(1, 3) should output "0.(3)" instead of "0.3333333333"
• convert(7, 11) should output "0.(63)" instead of "0.6363636364"
• convert(29. 12) should output "2.41(6)" instead of "2.4166666667"

My current code is at the end of the question, but it fails if there are non-repeating and repeating decimal places. Here's an example run including the debug output (commented print calls):

----> 29 / 12
5
appended 4
2
appended 1
8
index 2 ['29', 2, 8] result ['2.', '4', '(', '1']
repeating 8
['2.', '4', '(', '1', ')']

What am I doing wrong here?

---

My code:

def convert(numerator, denominator):
    #print("---->", numerator, "/", denominator)
    result = [str(numerator//denominator) + "."]
    subresults = [str(numerator)]
    numerator %= denominator
    while numerator != 0:
        #print(numerator)
        numerator *= 10
        result_digit, numerator = divmod(numerator, denominator)
        if numerator not in subresults:
            subresults.append(numerator)
            result.append(str(result_digit))
            #print("appended", result_digit)
        else:
            result.insert(subresults.index(numerator), "(")
            #print("index", subresults.index(numerator), subresults, "result", result)
            result.append(")")
            #print("repeating", numerator)
            break
    #print(result)
    return "".join(result)

Answer 1

Your code just needed some minor changes (see the comments below):

def convert(numerator, denominator):
    #print("---->", numerator, "/", denominator)
    result = [str(numerator//denominator) + "."]
    subresults = [numerator % denominator]          ### changed ###
    numerator %= denominator
    while numerator != 0:
        #print(numerator)
        numerator *= 10
        result_digit, numerator = divmod(numerator, denominator)
        result.append(str(result_digit))             ### moved before if-statement

        if numerator not in subresults:
            subresults.append(numerator)
            #print("appended", result_digit)

        else:
            result.insert(subresults.index(numerator) + 1, "(")   ### added '+ 1'
            #print("index", subresults.index(numerator), subresults, "result", result)
            result.append(")")
            #print("repeating", numerator)
            break
    #print(result)
    return "".join(result)