title: I keep getting an error called 'int' object has no attribute 'replace'
body: <p>For my code I don't need to replace numbers, only things like parenthesis and dashes and I thought I spec ifoed that in my code but it still doesnt work. Here is the code:</p>
  
  <pre><code>def standardize_phone_number(phone_number):
      phone_number = str(phone_number.replace('(', '')\
                           .replace(')', '')\
                           .replace(' ', '')\
                           .replace('-', ''))
  
      if not (phone_number.isdigit() and len(phone_number) == 10):
          return None
  
      if phone_number[0] == '(' and phone_number[4:6] == ')' and \
         phone_number[9] == '-' and len(phone_number) == 13:
          return phone_number.replace('(', '').replace(')', '-')
  
      if phone_number[3] == '-' and phone_number[7] == '-' and \
         len(phone_number) == 11:
          return phone_number.replace('-', '').replace('-', '')
  
      if phone_number[5] == ' ' and phone_number[9] == '-' and \
         len(phone_number) == 13:
          return phone_number.replace(' ', '').replace('-', '')
      else:
          return None
  print(standardize_phone_number(123-456-7890))
  </code></pre>