# Author: Rob Kremer

""" Asks for a valid phone number until one is entered.  Valid phone
numbers are 7 digits long, cannot have the first digit 0, and may
contain embedded blanks or dashes.
"""
repeat = True
while repeat:
    repeat = False
    phoneNum = input("Entry a valid phone 7-digit phone number: ")
    digitCount = 0
    first = True
    for c in phoneNum:   
        legalDigit = ((first and c>="1") or (not first and c>="0")) and c <="9"
        if legalDigit:
            digitCount += 1
        if not (legalDigit or c==" " or c=="-"):
            repeat = True
            break;
        first = False
    if digitCount!=7:
        repeat = True
        
print("Thank you; valid phone number entered.")