Phone numbers, Python Programming

Phone numbers in the United States consist of 10 digits, sometimes formatted with punctuation and spaces. Write a program that prompts for a phone number and determines whether or not it is a valid 10-digit number by ignoring any punctuation. Do this by writing a function that takes the phone number string as a parameter and returns True if it is valid, False if not. (Hint: use a for loop to iterate over the string and increment a counter whenever you see a digit.)