File Extension

const re = new RegExp("\\.([A-Za-z0-9]+)$", "");
const input = "document.pdf";
const match = input.match(re);
console.log(match ? match[0] : null);

import re

pattern = re.compile(r"\.([A-Za-z0-9]+)$")
input_text = "document.pdf"
for m in pattern.finditer(input_text):
    print(m.group(0))

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`\.([A-Za-z0-9]+)$`)
	input := `document.pdf`
	for _, match := range re.FindAllString(input, -1) {
		fmt.Println(match)
	}
}