prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  RFC: Only accept delimited string in DelimitedList
  `DelimitedList` accepts either a list or a delimited string (e.g. "foo,bar,baz").
  
  I'd like to make it more strict by only accepting a delimited list. Rather than adding a `strict` parameter, I'm thinking of dropping the whole "also accept a list" feature.
  
  Any reason to support both?
  
  I understand it inherits from `List` because once the string is parsed, it can be deserialized as a normal list. But are there cases where you'd expect either a list or a delimited string?
  
  </issue>
  <code>
  [start of src/webargs/fields.py]
  1 """Field classes.
  2 
  3 Includes all fields from `marshmallow.fields` in addition to a custom
  4 `Nested` field and `DelimitedList`.
  5 
  6 All fields can optionally take a special `location` keyword argument, which
  7 tells webargs where to parse the request argument from.
  8 
  9 .. code-block:: python
  10 
  11     args = {
  12         "active": fields.Bool(location="query"),
  13         "content_type": fields.Str(data_key="Content-Type", location="headers"),
  14     }
  15 
  16 Note: `data_key` replaced `load_from` in marshmallow 3.
  17 When using marshmallow 2, use `load_from`.
  18 """
  19 import marshmallow as ma
  20 
  21 # Expose all fields from marshmallow.fields.
  22 from marshmallow.fields import *  # noqa: F40
  23 from webargs.compat import MARSHMALLOW_VERSION_INFO
  24 from webargs.dict2schema import dict2schema
  25 
  26 __all__ = ["DelimitedList"] + ma.fields.__all__
  27 
  28 
  29 class Nested(ma.fields.Nested):
  30     """Same as `marshmallow.fields.Nested`, except can be passed a dictionary as
  31     the first argument, which will be converted to a `marshmallow.Schema`.
  32 
  33     .. note::
  34 
  35         The schema class here will always be `marshmallow.Schema`, regardless
  36         of whether a custom schema class is set on the parser. Pass an explicit schema
  37         class if necessary.
  38     """
  39 
  40     def __init__(self, nested, *args, **kwargs):
  41         if isinstance(nested, dict):
  42             nested = dict2schema(nested)
  43         super().__init__(nested, *args, **kwargs)
  44 
  45 
  46 class DelimitedList(ma.fields.List):
  47     """Same as `marshmallow.fields.List`, except can load from either a list or
  48     a delimited string (e.g. "foo,bar,baz").
  49 
  50     :param Field cls_or_instance: A field class or instance.
  51     :param str delimiter: Delimiter between values.
  52     :param bool as_string: Dump values to string.
  53     """
  54 
  55     delimiter = ","
  56 
  57     def __init__(self, cls_or_instance, delimiter=None, as_string=False, **kwargs):
  58         self.delimiter = delimiter or self.delimiter
  59         self.as_string = as_string
  60         super().__init__(cls_or_instance, **kwargs)
  61 
  62     def _serialize(self, value, attr, obj):
  63         ret = super()._serialize(value, attr, obj)
  64         if self.as_string:
  65             return self.delimiter.join(format(each) for each in ret)
  66         return ret
  67 
  68     def _deserialize(self, value, attr, data, **kwargs):
  69         try:
  70             ret = (
  71                 value
  72                 if ma.utils.is_iterable_but_not_string(value)
  73                 else value.split(self.delimiter)
  74             )
  75         except AttributeError:
  76             if MARSHMALLOW_VERSION_INFO[0] < 3:
  77                 self.fail("invalid")
  78             else:
  79                 raise self.make_error("invalid")
  80         return super()._deserialize(ret, attr, data, **kwargs)
  81
  [end of src/webargs/fields.py]
  </code>
  
  I need you to solve this issue by generating a single patch file that I can apply directly to this repository using git apply. Please respond with a single patch file in the following format.
  <patch>
  diff --git a/file.py b/file.py
  --- a/file.py
  +++ b/file.py
  @@ -1,27 +1,35 @@
   def euclidean(a, b):
  -    while b:
  -        a, b = b, a % b
  -    return a
  +    if b == 0:
  +        return a
  +    return euclidean(b, a % b)
   
   
   def bresenham(x0, y0, x1, y1):
       points = []
       dx = abs(x1 - x0)
       dy = abs(y1 - y0)
  -    sx = 1 if x0 < x1 else -1
  -    sy = 1 if y0 < y1 else -1
  -    err = dx - dy
  +    x, y = x0, y0
  +    sx = -1 if x0 > x1 else 1
  +    sy = -1 if y0 > y1 else 1
   
  -    while True:
  -        points.append((x0, y0))
  -        if x0 == x1 and y0 == y1:
  -            break
  -        e2 = 2 * err
  -        if e2 > -dy:
  -            err -= dy
  -            x0 += sx
  -        if e2 < dx:
  -            err += dx
  -            y0 += sy
  +    if dx > dy:
  +        err = dx / 2.0
  +        while x != x1:
  +            points.append((x, y))
  +            err -= dy
  +            if err < 0:
  +                y += sy
  +                err += dx
  +            x += sx
  +    else:
  +        err = dy / 2.0
  +        while y != y1:
  +            points.append((x, y))
  +            err -= dx
  +            if err < 0:
  +                x += sx
  +                err += dy
  +            y += sy
  +
  +    points.append((x, y))
       return points
  
  </patch>
golden_diff: diff --git a/src/webargs/fields.py b/src/webargs/fields.py
  --- a/src/webargs/fields.py
  +++ b/src/webargs/fields.py
  @@ -44,37 +44,35 @@
   
   
   class DelimitedList(ma.fields.List):
  -    """Same as `marshmallow.fields.List`, except can load from either a list or
  -    a delimited string (e.g. "foo,bar,baz").
  +    """A field which is similar to a List, but takes its input as a delimited
  +    string (e.g. "foo,bar,baz").
  +
  +    Like List, it can be given a nested field type which it will use to
  +    de/serialize each element of the list.
   
       :param Field cls_or_instance: A field class or instance.
       :param str delimiter: Delimiter between values.
  -    :param bool as_string: Dump values to string.
       """
   
  +    default_error_messages = {"invalid": "Not a valid delimited list."}
       delimiter = ","
   
  -    def __init__(self, cls_or_instance, delimiter=None, as_string=False, **kwargs):
  +    def __init__(self, cls_or_instance, delimiter=None, **kwargs):
           self.delimiter = delimiter or self.delimiter
  -        self.as_string = as_string
           super().__init__(cls_or_instance, **kwargs)
   
       def _serialize(self, value, attr, obj):
  -        ret = super()._serialize(value, attr, obj)
  -        if self.as_string:
  -            return self.delimiter.join(format(each) for each in ret)
  -        return ret
  +        # serializing will start with List serialization, so that we correctly
  +        # output lists of non-primitive types, e.g. DelimitedList(DateTime)
  +        return self.delimiter.join(
  +            format(each) for each in super()._serialize(value, attr, obj)
  +        )
   
       def _deserialize(self, value, attr, data, **kwargs):
  -        try:
  -            ret = (
  -                value
  -                if ma.utils.is_iterable_but_not_string(value)
  -                else value.split(self.delimiter)
  -            )
  -        except AttributeError:
  +        # attempting to deserialize from a non-string source is an error
  +        if not isinstance(value, (str, bytes)):
               if MARSHMALLOW_VERSION_INFO[0] < 3:
                   self.fail("invalid")
               else:
                   raise self.make_error("invalid")
  -        return super()._deserialize(ret, attr, data, **kwargs)
  +        return super()._deserialize(value.split(self.delimiter), attr, data, **kwargs)
  
verification_info: {"golden_diff": "diff --git a/src/webargs/fields.py b/src/webargs/fields.py\n--- a/src/webargs/fields.py\n+++ b/src/webargs/fields.py\n@@ -44,37 +44,35 @@\n \n \n class DelimitedList(ma.fields.List):\n-    \"\"\"Same as `marshmallow.fields.List`, except can load from either a list or\n-    a delimited string (e.g. \"foo,bar,baz\").\n+    \"\"\"A field which is similar to a List, but takes its input as a delimited\n+    string (e.g. \"foo,bar,baz\").\n+\n+    Like List, it can be given a nested field type which it will use to\n+    de/serialize each element of the list.\n \n     :param Field cls_or_instance: A field class or instance.\n     :param str delimiter: Delimiter between values.\n-    :param bool as_string: Dump values to string.\n     \"\"\"\n \n+    default_error_messages = {\"invalid\": \"Not a valid delimited list.\"}\n     delimiter = \",\"\n \n-    def __init__(self, cls_or_instance, delimiter=None, as_string=False, **kwargs):\n+    def __init__(self, cls_or_instance, delimiter=None, **kwargs):\n         self.delimiter = delimiter or self.delimiter\n-        self.as_string = as_string\n         super().__init__(cls_or_instance, **kwargs)\n \n     def _serialize(self, value, attr, obj):\n-        ret = super()._serialize(value, attr, obj)\n-        if self.as_string:\n-            return self.delimiter.join(format(each) for each in ret)\n-        return ret\n+        # serializing will start with List serialization, so that we correctly\n+        # output lists of non-primitive types, e.g. DelimitedList(DateTime)\n+        return self.delimiter.join(\n+            format(each) for each in super()._serialize(value, attr, obj)\n+        )\n \n     def _deserialize(self, value, attr, data, **kwargs):\n-        try:\n-            ret = (\n-                value\n-                if ma.utils.is_iterable_but_not_string(value)\n-                else value.split(self.delimiter)\n-            )\n-        except AttributeError:\n+        # attempting to deserialize from a non-string source is an error\n+        if not isinstance(value, (str, bytes)):\n             if MARSHMALLOW_VERSION_INFO[0] < 3:\n                 self.fail(\"invalid\")\n             else:\n                 raise self.make_error(\"invalid\")\n-        return super()._deserialize(ret, attr, data, **kwargs)\n+        return super()._deserialize(value.split(self.delimiter), attr, data, **kwargs)\n", "issue": "RFC: Only accept delimited string in DelimitedList\n`DelimitedList` accepts either a list or a delimited string (e.g. \"foo,bar,baz\").\r\n\r\nI'd like to make it more strict by only accepting a delimited list. Rather than adding a `strict` parameter, I'm thinking of dropping the whole \"also accept a list\" feature.\r\n\r\nAny reason to support both?\r\n\r\nI understand it inherits from `List` because once the string is parsed, it can be deserialized as a normal list. But are there cases where you'd expect either a list or a delimited string?\n", "before_files": [{"content": "\"\"\"Field classes.\n\nIncludes all fields from `marshmallow.fields` in addition to a custom\n`Nested` field and `DelimitedList`.\n\nAll fields can optionally take a special `location` keyword argument, which\ntells webargs where to parse the request argument from.\n\n.. code-block:: python\n\n    args = {\n        \"active\": fields.Bool(location=\"query\"),\n        \"content_type\": fields.Str(data_key=\"Content-Type\", location=\"headers\"),\n    }\n\nNote: `data_key` replaced `load_from` in marshmallow 3.\nWhen using marshmallow 2, use `load_from`.\n\"\"\"\nimport marshmallow as ma\n\n# Expose all fields from marshmallow.fields.\nfrom marshmallow.fields import *  # noqa: F40\nfrom webargs.compat import MARSHMALLOW_VERSION_INFO\nfrom webargs.dict2schema import dict2schema\n\n__all__ = [\"DelimitedList\"] + ma.fields.__all__\n\n\nclass Nested(ma.fields.Nested):\n    \"\"\"Same as `marshmallow.fields.Nested`, except can be passed a dictionary as\n    the first argument, which will be converted to a `marshmallow.Schema`.\n\n    .. note::\n\n        The schema class here will always be `marshmallow.Schema`, regardless\n        of whether a custom schema class is set on the parser. Pass an explicit schema\n        class if necessary.\n    \"\"\"\n\n    def __init__(self, nested, *args, **kwargs):\n        if isinstance(nested, dict):\n            nested = dict2schema(nested)\n        super().__init__(nested, *args, **kwargs)\n\n\nclass DelimitedList(ma.fields.List):\n    \"\"\"Same as `marshmallow.fields.List`, except can load from either a list or\n    a delimited string (e.g. \"foo,bar,baz\").\n\n    :param Field cls_or_instance: A field class or instance.\n    :param str delimiter: Delimiter between values.\n    :param bool as_string: Dump values to string.\n    \"\"\"\n\n    delimiter = \",\"\n\n    def __init__(self, cls_or_instance, delimiter=None, as_string=False, **kwargs):\n        self.delimiter = delimiter or self.delimiter\n        self.as_string = as_string\n        super().__init__(cls_or_instance, **kwargs)\n\n    def _serialize(self, value, attr, obj):\n        ret = super()._serialize(value, attr, obj)\n        if self.as_string:\n            return self.delimiter.join(format(each) for each in ret)\n        return ret\n\n    def _deserialize(self, value, attr, data, **kwargs):\n        try:\n            ret = (\n                value\n                if ma.utils.is_iterable_but_not_string(value)\n                else value.split(self.delimiter)\n            )\n        except AttributeError:\n            if MARSHMALLOW_VERSION_INFO[0] < 3:\n                self.fail(\"invalid\")\n            else:\n                raise self.make_error(\"invalid\")\n        return super()._deserialize(ret, attr, data, **kwargs)\n", "path": "src/webargs/fields.py"}]}