Fill in the function problem1. This function should return True if the input string is a valid phone number and False if not. We define a valid phone number as follows: First, it contains an optional area code (3 digits) followed by 7 digits.
Second, there could be one of several possible formats for the phone number, where the Xs are digits:
(XXX) XXX-
XXX-XXX-
XXX-
ANY other format should not count as a valid phone number. Spaces before or after an otherwise number is considered invalid.
Remember that (, ), - and . are special characters for regular expressions. To search for those characters, you need to precede them with a backslash: \( \), \-, \..
Because we are looking for the entire string to be a phone number, you can either use ^ and $ to force a match to be at the beginning and end of a string, or you can use fullmatch instead of match or search.
Where problem1 is : (you can assume import re is already there)
def problem1(searchstring):
"""
Match phone numbers.
:param searchstring: string
:return: True or False
"""
pass'