# The convert_phone_number function checks for a U.S. phone number format: XXX-XXX-XXXX (3 digits
# followed by a dash, 3 more digits followed by a dash, and 4 digits), and converts it to a more formal 
# format that looks like this: (XXX) XXX-XXXX. 
# Fill in the regular expression to complete this function.

#!/usr/bin/env python3

import re

def convert_phone_number(phone):
  result = re.sub(r"________", r"_____", phone)
  return result

print(convert_phone_number("My number is 212-345-9999.")) 
# My number is (212) 345-9999.
print(convert_phone_number("Please call 888-555-1234")) 
# Please call (888) 555-1234
print(convert_phone_number("123-123-12345")) 
# 123-123-12345
print(convert_phone_number("Phone number of Buckingham Palace is +44 303 123 7300")) 
# Phone number of Buckingham Palace is +44 303 123 7300
