  class Field(object):
      _creation_counter = 0
  
      default_error_messages = {
          'required': _("This field is required."),
          'null': _("This field may not be null.")
      }
      default_validators = []
      default_empty_html = empty
      initial = None
  
 
</s> remove         'blank': _("This field may not be blank."),
        'max_length': _("Ensure this field has no more than {max_length} characters."),
        'min_length': _("Ensure this field has at least {min_length} characters.")
 </s> add         'blank': _('This field may not be blank.'),
        'max_length': _('Ensure this field has no more than {max_length} characters.'),
        'min_length': _('Ensure this field has at least {min_length} characters.') </s> remove         'required': _("This field is required."),
        'does_not_exist': _("Invalid pk \"{pk_value}\" - object does not exist."),
        'incorrect_type': _("Incorrect type. Expected pk value, received {data_type}."),
 </s> add         'required': _('This field is required.'),
        'does_not_exist': _('Invalid pk "{pk_value}" - object does not exist.'),
        'incorrect_type': _('Incorrect type. Expected pk value, received {data_type}.'), </s> remove     missing_message = _("This field is required.")
 </s> add     missing_message = _('This field is required.') </s> remove         'required': _("This field is required."),
        'no_match': _("Invalid hyperlink - No URL match."),
        'incorrect_match': _("Invalid hyperlink - Incorrect URL match."),
        'does_not_exist': _("Invalid hyperlink - Object does not exist."),
        'incorrect_type': _("Incorrect type. Expected URL string, received {data_type}."),
 </s> add         'required': _('This field is required.'),
        'no_match': _('Invalid hyperlink - No URL match.'),
        'incorrect_match': _('Invalid hyperlink - Incorrect URL match.'),
        'does_not_exist': _('Invalid hyperlink - Object does not exist.'),
        'incorrect_type': _('Incorrect type. Expected URL string, received {data_type}.'), </s> remove         'invalid': _("`{input}` is not a valid boolean.")
 </s> add         'invalid': _('`{input}` is not a valid boolean.')
        'required': _('This field is required.'),
        'null': _('This field may not be null.')
  class Field(object):
      _creation_counter = 0
  
      default_error_messages = {
        'required': _('This field is required.'),
        'null': _('This field may not be null.')
        'required': _('This field is required.'),
        'null': _('This field may not be null.')
      }
      default_validators = []
      default_empty_html = empty
      initial = None
  
keep keep keep keep replace replace keep keep keep keep keep
 prefer single quotes in source and double quotes in user visible strings; add some missing full stops to user visible strings 
rest_framework/fields.py