Decimal to roman python

Question

I'm a beginner as you can see and I would like to know how I can improve my code. Studying for 6 months now. Thank you.

roman_dict = {1: 'I', 4: 'IV', 5: 'V', 9: 'IX', 10: 'X', 40: 'XL', 50: 'L', 90: 'XC', 100: 'C', 400: 'CD',
 500: 'D', 900: 'CM', 1000: 'M'}
divide_list = [1000, 100, 10, 1]
def not_in_dict(fixed_decimal, divide_num):
 sub_count = 0
 sub_roman_multi = roman_dict[divide_num]
 temp_decimal = fixed_decimal
 while temp_decimal not in roman_dict:
 temp_decimal -= divide_num
 sub_count += 1
 return roman_dict[temp_decimal]+(sub_count*sub_roman_multi)
def decimal_to_roman(decimal):
 original_decimal = decimal
 roman = ""
 for divide_num in divide_list:
 if decimal >= divide_num:
 reminder = decimal//divide_num
 if(reminder >= 1) and ((reminder*divide_num) in roman_dict):
 roman += roman_dict[(reminder*divide_num)]
 decimal -= reminder*divide_num
 else:
 roman += not_in_dict(reminder*divide_num, divide_num)
 decimal -= (reminder*divide_num)
 return str(original_decimal)+' = '+roman

Answer 1

If you use a list of tuples instead of a dictionary and reverse the order, you can simply iterate over it. Your while loop also becomes a lot easier to understand and there is no longer any need to outsource it to another function that returns the literal and its count.

Instead of manually adding strings (something you should basically never do in in Python), use str.join.

ROMAN_LITERALS = [(1000, 'M'), (900, 'CM'), (500, 'D'), (400, 'CD'), (100, 'C'),
 (90, 'XC'), (50, 'L'), (40, 'XL'), (10, 'X'), (9, 'IX'),
 (5, 'V'), (4, 'IV'), (1, 'I')]
def decimal_to_roman(x):
 out = []
 for value, literal in ROMAN_LITERALS:
 while x >= value:
 x -= value
 out.append(literal)
 return "".join(out)

Instead of the while loop you can also use integer division like you did:

def decimal_to_roman(x):
 out = []
 for value, literal in ROMAN_LITERALS:
 n = x // value # will be 0 if value is too large
 out.extend([literal] * n) # will not do anything if n == 0
 x -= n * value # will also not do anything if n == 0
 return "".join(out)

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