CODEWITHSUNDEEP
pythonroman-numerals
ifaminsi
ifaminsi

Reputation: 181

convert roman to number got index out of range error

I am new to python. Trying to convert roman to numbers. Everything works perfect but when I input some roman terms I got index error. Please trace out the error and correct me.

def roman(x):
    x=list(x)
    print(x)
    s=0
    val=[['I',1],['V',5],['X',10],['L',50],['C',100],['D',500],['M',1000]]
    val=dict(val)


while x:

    a=val[x[0]]
    b=val[x[1]]
    print('a----',a)
    print('b----',b)
    if (a>=b):
        s=s+a
        x=x[1:]
    else:
        s=s+b-a
        x=x[2:]
return s

x=input("Enter roman characters to convert to decimal: ")
x=x.upper()
a=roman(x)
print(a)

When I input 'IXC, IVX' these terms I got index error. Why it is not accepting 'I'. The output I got is shown:

enter image description here

Upvotes: 1

Views: 367

Answers (1)

Sharad
Sharad

Reputation: 10612

Can you instead try the roman package:

>>> import roman
>>> roman.fromRoman('X')
10
>>> roman.fromRoman('IV')
4
>>> roman.fromRoman('V')
5
>>> roman.fromRoman('M')
1000
>>> roman.fromRoman('L')
50
>>>

As for the error, Jonathan has correctly pointed out:

>>> roman.fromRoman('IXC')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/sharad/trials/udev_env/lib/python3.5/site-packages/roman.py", line 72, in fromRoman
    raise InvalidRomanNumeralError('Invalid Roman numeral: %s' % s)
roman.InvalidRomanNumeralError: Invalid Roman numeral: IXC
>>> 

>>> roman.fromRoman('IVX')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/sharad/trials/udev_env/lib/python3.5/site-packages/roman.py", line 72, in fromRoman
    raise InvalidRomanNumeralError('Invalid Roman numeral: %s' % s)
roman.InvalidRomanNumeralError: Invalid Roman numeral: IVX
>>>

The IndexError: list index out of range is due to:

In the while loop,

iteration#1
a = 1
b = 10
1 >= 10 => false

so, the code enters the else block:

x=x[2:] # x = ['C'] for IXC as input OR x = ['X'] for IVX as input

iteration#2

# x only has a single element
a=val[x[0]] # success
b=val[x[1]] # crashes, since x only has a single element

Upvotes: 2

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