def isPhoneNumber(text):
    if len(text) != 12:
        return False  # not phone number-sized
    for i in range(0, 3):
        if not text[i].isdecimal():
            return False  # not an area code
    if text[3] != '-':
        return False  # does not have first hyphen
    for i in range(4, 7):
        if not text[i].isdecimal():
            return False  # does not have first 3 digits
    if text[7] != '-':
        return False  # does not have second hyphen
    for i in range(8, 12):
        if not text[i].isdecimal():
            return False  # does not have last 4 digits
    return True  # "text" is a phone number!

print('415-555-4242 is a phone number:')
print(isPhoneNumber('415-555-4242'))
print('Moshi moshi is a phone number:')
print(isPhoneNumber('Moshi moshi'))