prompt: You will be provided with a partial code base and an issue statement explaining a problem to resolve.
  <issue>
  Copying items not work correctly with list values
  > > item = Item()
  > > item['some_field'] = []
  > > 
  > > c_item = Item(item)
  > > c_item['some_field'].append(1)
  > > 
  > > print item['some_field'], c_item['some_field']
  > > [1] [1]
  
  
  </issue>
  <code>
  [start of scrapy/item.py]
  1 """
  2 Scrapy Item
  3 
  4 See documentation in docs/topics/item.rst
  5 """
  6 
  7 from pprint import pformat
  8 from collections import MutableMapping
  9 
  10 from abc import ABCMeta
  11 import six
  12 
  13 from scrapy.utils.trackref import object_ref
  14 
  15 
  16 class BaseItem(object_ref):
  17     """Base class for all scraped items."""
  18     pass
  19 
  20 
  21 class Field(dict):
  22     """Container of field metadata"""
  23 
  24 
  25 class ItemMeta(ABCMeta):
  26 
  27     def __new__(mcs, class_name, bases, attrs):
  28         classcell = attrs.pop('__classcell__', None)
  29         new_bases = tuple(base._class for base in bases if hasattr(base, '_class'))
  30         _class = super(ItemMeta, mcs).__new__(mcs, 'x_' + class_name, new_bases, attrs)
  31 
  32         fields = getattr(_class, 'fields', {})
  33         new_attrs = {}
  34         for n in dir(_class):
  35             v = getattr(_class, n)
  36             if isinstance(v, Field):
  37                 fields[n] = v
  38             elif n in attrs:
  39                 new_attrs[n] = attrs[n]
  40 
  41         new_attrs['fields'] = fields
  42         new_attrs['_class'] = _class
  43         if classcell is not None:
  44             new_attrs['__classcell__'] = classcell
  45         return super(ItemMeta, mcs).__new__(mcs, class_name, bases, new_attrs)
  46 
  47 
  48 class DictItem(MutableMapping, BaseItem):
  49 
  50     fields = {}
  51 
  52     def __init__(self, *args, **kwargs):
  53         self._values = {}
  54         if args or kwargs:  # avoid creating dict for most common case
  55             for k, v in six.iteritems(dict(*args, **kwargs)):
  56                 self[k] = v
  57 
  58     def __getitem__(self, key):
  59         return self._values[key]
  60 
  61     def __setitem__(self, key, value):
  62         if key in self.fields:
  63             self._values[key] = value
  64         else:
  65             raise KeyError("%s does not support field: %s" %
  66                 (self.__class__.__name__, key))
  67 
  68     def __delitem__(self, key):
  69         del self._values[key]
  70 
  71     def __getattr__(self, name):
  72         if name in self.fields:
  73             raise AttributeError("Use item[%r] to get field value" % name)
  74         raise AttributeError(name)
  75 
  76     def __setattr__(self, name, value):
  77         if not name.startswith('_'):
  78             raise AttributeError("Use item[%r] = %r to set field value" %
  79                 (name, value))
  80         super(DictItem, self).__setattr__(name, value)
  81 
  82     def __len__(self):
  83         return len(self._values)
  84 
  85     def __iter__(self):
  86         return iter(self._values)
  87 
  88     __hash__ = BaseItem.__hash__
  89 
  90     def keys(self):
  91         return self._values.keys()
  92 
  93     def __repr__(self):
  94         return pformat(dict(self))
  95 
  96     def copy(self):
  97         return self.__class__(self)
  98 
  99 
  100 @six.add_metaclass(ItemMeta)
  101 class Item(DictItem):
  102     pass
  103
  [end of scrapy/item.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/scrapy/item.py b/scrapy/item.py
  --- a/scrapy/item.py
  +++ b/scrapy/item.py
  @@ -6,6 +6,7 @@
   
   from pprint import pformat
   from collections import MutableMapping
  +from copy import deepcopy
   
   from abc import ABCMeta
   import six
  @@ -96,6 +97,13 @@
       def copy(self):
           return self.__class__(self)
   
  +    def deepcopy(self):
  +        """Return a `deep copy`_ of this item.
  +
  +        .. _deep copy: https://docs.python.org/library/copy.html#copy.deepcopy
  +        """
  +        return deepcopy(self)
  +
   
   @six.add_metaclass(ItemMeta)
   class Item(DictItem):
  
verification_info: {"golden_diff": "diff --git a/scrapy/item.py b/scrapy/item.py\n--- a/scrapy/item.py\n+++ b/scrapy/item.py\n@@ -6,6 +6,7 @@\n \n from pprint import pformat\n from collections import MutableMapping\n+from copy import deepcopy\n \n from abc import ABCMeta\n import six\n@@ -96,6 +97,13 @@\n     def copy(self):\n         return self.__class__(self)\n \n+    def deepcopy(self):\n+        \"\"\"Return a `deep copy`_ of this item.\n+\n+        .. _deep copy: https://docs.python.org/library/copy.html#copy.deepcopy\n+        \"\"\"\n+        return deepcopy(self)\n+\n \n @six.add_metaclass(ItemMeta)\n class Item(DictItem):\n", "issue": "Copying items not work correctly with list values\n> > item = Item()\n> > item['some_field'] = []\n> > \n> > c_item = Item(item)\n> > c_item['some_field'].append(1)\n> > \n> > print item['some_field'], c_item['some_field']\n> > [1] [1]\n\n", "before_files": [{"content": "\"\"\"\nScrapy Item\n\nSee documentation in docs/topics/item.rst\n\"\"\"\n\nfrom pprint import pformat\nfrom collections import MutableMapping\n\nfrom abc import ABCMeta\nimport six\n\nfrom scrapy.utils.trackref import object_ref\n\n\nclass BaseItem(object_ref):\n    \"\"\"Base class for all scraped items.\"\"\"\n    pass\n\n\nclass Field(dict):\n    \"\"\"Container of field metadata\"\"\"\n\n\nclass ItemMeta(ABCMeta):\n\n    def __new__(mcs, class_name, bases, attrs):\n        classcell = attrs.pop('__classcell__', None)\n        new_bases = tuple(base._class for base in bases if hasattr(base, '_class'))\n        _class = super(ItemMeta, mcs).__new__(mcs, 'x_' + class_name, new_bases, attrs)\n\n        fields = getattr(_class, 'fields', {})\n        new_attrs = {}\n        for n in dir(_class):\n            v = getattr(_class, n)\n            if isinstance(v, Field):\n                fields[n] = v\n            elif n in attrs:\n                new_attrs[n] = attrs[n]\n\n        new_attrs['fields'] = fields\n        new_attrs['_class'] = _class\n        if classcell is not None:\n            new_attrs['__classcell__'] = classcell\n        return super(ItemMeta, mcs).__new__(mcs, class_name, bases, new_attrs)\n\n\nclass DictItem(MutableMapping, BaseItem):\n\n    fields = {}\n\n    def __init__(self, *args, **kwargs):\n        self._values = {}\n        if args or kwargs:  # avoid creating dict for most common case\n            for k, v in six.iteritems(dict(*args, **kwargs)):\n                self[k] = v\n\n    def __getitem__(self, key):\n        return self._values[key]\n\n    def __setitem__(self, key, value):\n        if key in self.fields:\n            self._values[key] = value\n        else:\n            raise KeyError(\"%s does not support field: %s\" %\n                (self.__class__.__name__, key))\n\n    def __delitem__(self, key):\n        del self._values[key]\n\n    def __getattr__(self, name):\n        if name in self.fields:\n            raise AttributeError(\"Use item[%r] to get field value\" % name)\n        raise AttributeError(name)\n\n    def __setattr__(self, name, value):\n        if not name.startswith('_'):\n            raise AttributeError(\"Use item[%r] = %r to set field value\" %\n                (name, value))\n        super(DictItem, self).__setattr__(name, value)\n\n    def __len__(self):\n        return len(self._values)\n\n    def __iter__(self):\n        return iter(self._values)\n\n    __hash__ = BaseItem.__hash__\n\n    def keys(self):\n        return self._values.keys()\n\n    def __repr__(self):\n        return pformat(dict(self))\n\n    def copy(self):\n        return self.__class__(self)\n\n\n@six.add_metaclass(ItemMeta)\nclass Item(DictItem):\n    pass\n", "path": "scrapy/item.py"}]}