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In this post, we will see how to convert roman number to integer in python.

## How to Convert Roman Number to Integer in Python

There are multiple ways in which numbers can be represented in the world of Python programming. Roman literals are one such approach to representing numbers in Python. Often times there is a need to convert one type of representation to another for the purpose of simplifying calculations and to allow ease of using several functions on the data.

This tutorial demonstrates the different ways available to convert roman number to integer in python.

##### What is a roman number in Python?

Roman literals follow the same rules in Python as that in general mathematics. Let us quickly brush up on the characters utilized to represent the different numbers and the rules that need to be followed in accordance with naming.

The general naming convention associated with roman literals is given below, and the same will also be adhered to while making use of roman numbers in Python.

Numeral | Value |
---|---|

I | 1 |

V | 5 |

X | 10 |

L | 50 |

C | 100 |

D | 500 |

M | 1000 |

Moreover, the rules to keep in mind when representing roman literals as a number are mentioned below for a clearer understanding of the user.

- The character
`I`

refers to the number`1`

when utilized individually. It can only be utilized three times in one go. This means that the number`4`

cannot be represented as`IIII`

. - It can be utilized as a prefix to letters like
`V`

and`X`

to denote numbers`4`

and`9`

respectively. - Similarly, the sign
`X`

, which is for the number`10`

initially, when as a suffix to`L`

and`C`

makes it represent the numbers`60`

and`110`

respectively. - Similarly, the sign
`C`

, which is for the number`100`

initially, when as a suffix to`D`

and`M`

makes it represent the numbers`600`

and`1100`

respectively.

Now that we have covered the generation of roman number denotations, let us move on to see the different approaches that can be utilized in completing the task of converting roman numbers to integers in python.

## How to convert roman number to integer in python?

There are multiple ways of converting roman number to integer in Python, ranging from utilizing manually created user-defined functions to utilizing certain unpopular libraries, all of which will be explained in the article below.

### Using the `if...else`

statement to convert roman number to integer in Python.

The `if...else`

statement is one of the simplest decision-making statements. It contains different blocks of code and a certain condition is tested to check whether the given block of code would get executed or not.

The following code uses the `if...else`

statement to convert roman number to integer in Python.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 |
def RL(x): if (x == 'I'): return 1 if (x == 'V'): return 5 if (x == 'X'): return 10 if (x == 'L'): return 50 if (x == 'C'): return 100 if (x == 'D'): return 500 if (x == 'M'): return 1000 return -1 def RomtoInt(str): a = 0 i = 0 while (i < len(str)): x1 = RL(str[i]) if (i + 1 < len(str)): x2 = RL(str[i + 1]) if (x1 >= x2): a = a + x1 i = i + 1 else: a = a + x2 - x1 i = i + 2 else: a = a + x1 i = i + 1 return a print(RomtoInt("CIV")) |

The above code provides the following output:

## Further reading:

### Using classes and a dictionary to convert roman number to integer in Python.

Python is one of the most popular examples of Objected Oriented Programming (OOP) language out there, along with C++. Therefore, just like its rival, Python also supports and makes use of the concept of Classes. Almost every single thing that you see in a Python code can be deemed an object, along with its method and properties. Classes are just an approach or a blueprint to create these objects in Python.

Along with the use of classes, we will also utilize a Dictionary. A dictionary is one of the four pre-defined data types in Python that can be utilized to store data. A dictionary usually takes in the data in the form of `key:value`

pairs, which makes it excellent for storing the data on the conversion of roman literals to integers.

The following code makes use of classes and a dictionary to convert roman number to integer in Python.

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class sol: def RomtoInt(self, s): x = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000} y = 0 for i in range(len(s)): if i > 0 and x[s[i]] > x[s[i - 1]]: y += x[s[i]] - 2 * x[s[i - 1]] else: y += x[s[i]] return y print(sol().RomtoInt('CIV')) |

The above code provides the following output:

### Using the `roman`

module to convert roman number to integer in Python.

Some newer versions of Python 3 support the `roman`

module that provides functions that smoothen the process of conversion between roman numbers and other data types.

The `roman`

module first needs to be installed in the system and then can be simply imported to the code which grants us access to the functions provided by this module. This module can simply be installed with the `pip`

command.

1 2 3 |
pip install roman |

After installing the `roman`

module, we can move on to implementing the functions of this module to achieve the task at hand. For this, we will make use of the `roman.fromRoman()`

function.

The following code uses the `roman`

module to convert roman number to integer in Python.

1 2 3 4 5 |
import roman x=roman.fromRoman("CIV") print(x) |

The above code provides the following output:

It is important to note that this function is accurate in converting roman numbers to integer with the value varying between `0-5000`

. When it comes to numbers higher than that, then the accuracy of this function might dip down. In those cases, it is best to create a user-defined function and implement that.

## Conclusion

This tutorial brushes up on the concept of roman numbers in Python and emphasizes providing a detailed explanation of the different ways available to convert roman number to integer in Python.

The article takes three unique approaches to implement the task given at hand, with two of those having to create a user-defined function, and the third using a straight-up `module`

inherited function. In case of the value of numbers is too high, it is always recommended to create user-defined functions and implement them instead of depending on functions from the `roman`

library.