code: def _copy_core_fields_only(inobj):
      
      numobj = PhoneNumber()
      numobj.country_code = inobj.country_code
      numobj.national_number = inobj.national_number
      if inobj.extension is not None and len(inobj.extension) > 0:
          numobj.extension = inobj.extension
      if inobj.italian_leading_zero:
          numobj.italian_leading_zero = True
          # This field is only relevant if there are leading zeros at all.
          numobj.number_of_leading_zeros = inobj.number_of_leading_zeros
          if numobj.number_of_leading_zeros is None:
              # No number set is implicitly a count of 1; make it explicit.
              numobj.number_of_leading_zeros = 1
      return numobj
docs: Returns a new phone number containing only the fields needed to uniquely
      identify a phone number, rather than any fields that capture the context in
      which the phone number was created.