Change number string 1000 to 1.000?

Question

Python

Good afternoon. I would like to know how you can change the number string of the number 1000 to 1.000.

Answer 1

txt = "1000"

x = txt.replace("1000", "1.000")

print  (x)

Answer 2

a = '1000'
print(a[0] + '.' + a[1:])

Answer 3

import re

print(re.sub(r'(?<!^)(?=(\d{3})+$)', r'.', "12345673456456456"))

#Output:  12.345.673.456.456.456