InvalidOperation: [<class 'decimal.ConversionSyntax'>] in Lambda function python

Question

I have a sentence with plain numbers and ordinal numbers and I wanted to convert ordinal digits to words like 2 nd to Second, 56 th to Fifty sixth. I used the library num2words and below code works perfectly.

import num2words
text = "ordinal numbers are like as 42 nd, 67 th, and 5 th and plain numbers such as 1, 2, 3."
numbers = re.findall('(\d+ )[st|nd|rd|th]', text)
numbers
for n in numbers:
    ordinalAsString = num2words.num2words(n, ordinal=True)
    print(ordinalAsString)
    #forty-second
    #sixty-seventh
    #fifth

Now I want to create a lambda function such that,

sentence = "ordinal numbers are like as 42 nd, 67 th, and 5 th and plain numbers such as 1, 2, 3."
o/p sentence = "ordinal numbers are like as fourty-second, sixty-seventh, and fifth and plain numbers such as 1, 2, 3."

I wrote the function like this,

sentence = re.sub(r"(\d+ )[st|nd|rd|th]", lambda x: num2words.num2words(str(x), ordinal=True), sentence)

But that throws an error like,

InvalidOperation: [<class 'decimal.ConversionSyntax'>]

What is wrong in the code?

Answer 1

There are two problems:

1. Your regular expression isn't correctly matching the suffix, only the first letter of the suffix. [st|nd|rd|th] matches exactly one of the characters inside the brackets; duplicates are ignored, so it's equivalent to [st|ndrh] , with the | treated as a character to match like each of the letters. Use r"(\\d+ )(?:st|nd|rd|th)" instead; the | inside the non-capture group (?:...) does work to separate the 4 patterns st , nd , rd , and th .

2. The callable passed to re.sub takes a Match object as its argument. You need to use its group method to extract the captured sting. lambda x: num2words.num2words(x.group(1), ordinal=True) .