Converting number to roman numerals

[jagasrik]

Hi i have been trying to convert number to roman numerals all day but no luck, i know there is a readily available codes on internet with different algorithm, but i am trying a different approach(algorithm), which appears for me to mainly deal with differences.

my algorithm is below :

Example #1
x = 36
Answer:XXXVI

Iteration #	Decimal number (x)	Highest decimal value (v)	Highest roman numeral (n)	Temporary result 1 36 10 X X 2 26 10 X XX 3 16 10 X XXX 4 6 5 V XXXV 5 1 1 I XXXVI

Example #2
x = 2012
Answer: MMXII

Iteration #	Decimal number (x)	Highest decimal value (v)	Highest roman numeral (n)	Temporary result 1 2012 1000 M M 2 1012 1000 M MM 3 12 10 X MMX 4 2 1 I MMXI 5 1 1 I MMXII

Example #3
x = 1996
Answer: MCMXCVI

Iteration #	Decimal number (x)	Highest decimal value (v)	Highest roman numeral (n)	Temporary result 1 1996 1000 M M 2 996 900 CM MCM 3 96 90 XC MCMXC 4 6 5 V MCMXCV 5 1 1 I MCMXCVI

So far i have tried to implement this method like this in the below code:

class roman_num(): def num_conv(number): h_num= [1,4,5,9,10,40,50,90,100,400,500,900,1000] Rom_num= ['I','IV','V','IX','X','XL','L','XC','C','CD','D','CM','M'] h_num_rev = h_num h_num_rev.reverse() Rom_num_rev = Rom_num Rom_num_rev.reverse() var_rom=[] var_num=[] num=number for ind,val in enumerate(h_num_rev): num-=val print('In for loop ',num,ind,val) while ((num>=0) and (num>val)): var_num.append(val) num-=val print('In while loop ',num,ind,val) if(num<0): break if(num<0): num=number if(num==1): var_num.append(1) return(var_num) print(roman_num.num_conv(36))

it is just for practice, i have just started with python, i know i am no where near success, any help would be appreciated to implement.

[Larz60+]

here are some packages you can look at: https://pypi.org/search/?q=roman
this may be useful: https://www.mathsisfun.com/roman-numerals.html

[deanhystad]

Your Roman Numerals are in the wrong order. You provided a great example for how to solve the problem, then you wrote code that completely ignores the example.

In your example the first thing you did was find out how many 1000's there are in the number. For each 1000 you subtracted 1000 from the number and added 'M' to the Roman Numeral. Then you repeated this for the next lower value numeral (900 and CM). Repeat for every roman numeral in order of decreasing value until the remaining number is zero.

In your program you do the opposite. You start with the lowest value numeral work your way up. You know how to do this, don't freeze up just because you are now writing the algorithm in Python.

Maybe that is what you need, a written algorithm that can direct your coding.

def roman_numeral(number): # Map of roman numerals and values ordered in decreasing value. NUMERALS = {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'} # Start with an empty string retval = '' # Starting with the highest value, loop through all numerals ...: # While number is >= value, subtract value from number and add numeral to retval ... return retval

Next time write the comments yourself. If you have a hard time writing the comments it means you don't understand the problem. If you cannot write a good description of the algorithm you cannot write a program.

[voidptr]

From Wikipedia
https://en.wikipedia.org/wiki/Roman_numerals

Complete the code at (...) and you should be good to go.

:)

PS, of course it should be a class with converters, and the dictionary should be a class variable and etc. ...

def roman_numeral(n): dntor = { 3000:'MMM', 2000:'MM', 1000:'M', 900:'CM', 800:'DCCC', 700:'DCC', 600:'DC', 500:'D', 400:'CD', 300:'CCC', 200:'CC', 100:'C', 90:'XC', 80:'LXXX', 70:'LXX', 60:'LX', 50:'L', 40:'XL', 30:'XXX', 20:'XX', 10:'X', 9:'IX', 8:'VIII', 7:'VII', 6:'VI', 5:'V', 4:'IV', 3:'III', 2:'II', 1:'I', 0:'' } assert(0 < n < 4000) x = n%10 rs = dntor[x] n -= x #... assert(n==0) return rs

[jagasrik]

Your Roman Numerals are in the wrong order. You provided a great example for how to solve the problem, then you wrote code that completely ignores the example.

In your example the first thing you did was find out how many 1000's there are in the number. For each 1000 you subtracted 1000 from the number and added 'M' to the Roman Numeral. Then you repeated this for the next lower value numeral (900 and CM). Repeat for every roman numeral in order of decreasing value until the remaining number is zero.

In your program you do the opposite. You start with the lowest value numeral work your way up. You know how to do this, don't freeze up just because you are now writing the algorithm in Python.

Maybe that is what you need, a written algorithm that can direct your coding.

def roman_numeral(number): # Map of roman numerals and values ordered in decreasing value. NUMERALS = {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'} # Start with an empty string retval = '' # Starting with the highest value, loop through all numerals ...: # While number is >= value, subtract value from number and add numeral to retval ... return retval

Next time write the comments yourself. If you have a hard time writing the comments it means you don't understand the problem. If you cannot write a good description of the algorithm you cannot write a program.

Thanks a lot, it took me lot of time to figure it out, but was totally very useful tips, i will follow this in future.
Finally i was able to do it myself. Many thanks for giving me clarity, here is my code.

def roman_numeral(num): # Map of roman numerals and values ordered in decreasing value. NUMERALS = {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'} # Start with an empty string #retval = [] retval='' #num = 1996 # Starting with the highest value, loop through all numerals for i in NUMERALS: var=num-i print('In for loop ',i,' ',num,' ',var) # If number is >= value, subtract value from number and add numeral to retval if(var>=0): #retval.append(NUMERALS[i]) retval=retval+NUMERALS[i] while (var>=i): #retval.append(NUMERALS[i]) retval=retval+NUMERALS[i] var-=i print('In While loop ',i,' ',num,' ', var, ' ',retval ) num=var return retval roman_numeral(36)

---

From Wikipedia
https://en.wikipedia.org/wiki/Roman_numerals

Complete the code at (...) and you should be good to go.

:)

PS, of course it should be a class with converters, and the dictionary should be a class variable and etc. ...

def roman_numeral(n): dntor = { 3000:'MMM', 2000:'MM', 1000:'M', 900:'CM', 800:'DCCC', 700:'DCC', 600:'DC', 500:'D', 400:'CD', 300:'CCC', 200:'CC', 100:'C', 90:'XC', 80:'LXXX', 70:'LXX', 60:'LX', 50:'L', 40:'XL', 30:'XXX', 20:'XX', 10:'X', 9:'IX', 8:'VIII', 7:'VII', 6:'VI', 5:'V', 4:'IV', 3:'III', 2:'II', 1:'I', 0:'' } assert(0 < n < 4000) x = n%10 rs = dntor[x] n -= x #... assert(n==0) return rs

Thanks for helping hand, finally i solved it with the help of other comment suggestion.

[deanhystad]

I would do this:

 retval = '' for numval, numstr in NUMERALS.items(): # returns key and value from dictionary while num >= numval: num -= numval retval += numstr return retval

Python can be amazing in its brevity.

[voidptr]

this is it for me :)

def roman_numeral(n): dntor = { 3000:'MMM', 2000:'MM', 1000:'M', 900:'CM', 800:'DCCC', 700:'DCC', 600:'DC', 500:'D', 400:'CD', 300:'CCC', 200:'CC', 100:'C', 90:'XC', 80:'LXXX', 70:'LXX', 60:'LX', 50:'L', 40:'XL', 30:'XXX', 20:'XX', 10:'X', 9:'IX', 8:'VIII', 7:'VII', 6:'VI', 5:'V', 4:'IV', 3:'III', 2:'II', 1:'I', 0:'' } assert(0 < n < 4000) x = n%10 rs = dntor[x] n -= x x = n%100 rs = dntor[x] + rs n -= x x = n%1000 rs = dntor[x] + rs n -= x x = n%10000 rs = dntor[x] + rs n -= x assert(n==0) return rs #------- s = roman_numeral(100) s = roman_numeral(3999)