added newitem with new item model and fields

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40867

scrapy/trunk/scrapy/contrib/newitem/__init__.py

@@ -0,0 +1,2 @@
+from scrapy.contrib.newitem.models import Item
+from scrapy.contrib.newitem.fields import *

scrapy/trunk/scrapy/contrib/newitem/fields.py

@@ -1,15 +1,31 @@
+import datetime
+import decimal
 import re
 
+
 class ItemFieldValueError(Exception):
     pass
 
 
 class ItemField(object):
-    def __init__(self, required=False):
+    def __init__(self, required=False, default=None):
         self.required = required
+        self.default = default
 
     def to_python(self, value):
-        pass
+        """
+        Converts the input value into the expected Python data type.
+        Subclasses should override this.
+        """
+        return value
+
+    def from_list(self, list):
+        "Converts the input list into the expected Python data type."
+        return self.to_python(list.join(''))
+
+    def default_value(self):
+        "Returns the default value for this field"
+        return self.default or self.to_python(None)
 
 
 class BooleanItemField(ItemField):

scrapy/trunk/scrapy/contrib/newitem/models.py

@@ -0,0 +1,42 @@
+from scrapy.contrib.newitem.fields import ItemField
+
+
+class Item(object):
+    """
+    This is the base class for all scraped items.
+    """
+
+    def __init__(self):
+        self._values = {}
+        self._fields = self._get_fields()
+
+    def _get_fields(self):
+        return dict(i for i in self.__class__.__dict__.iteritems() if
+                    isinstance(i[1], ItemField))
+
+    def __setattr__(self, name, value):
+        if not name.startswith('_') and name in self._fields.keys():
+            self._values[name] = self._fields[name].to_python(value)
+        else:
+            # for now setting values that are not fields is permitted
+            object.__setattr__(self, name, value)
+
+    def __getattribute__(self, name):
+        if not name.startswith('_') and name in self._fields.keys():
+            try:
+                return self._values[name]
+            except KeyError:
+                # what to to in this case?
+                # maybe return a default value:
+                # return self._fields[name].default_value()
+                return None
+        else:
+            return object.__getattribute__(self, name)
+
+    def __repr__(self):
+        """
+        Generate the following format so that items can be deserialized
+        easily: ClassName({'attrib': value, ...})
+        """
+        reprdict = dict((field, getattr(self, field)) for field in self._fields)
+        return "%s(%s)" % (self.__class__.__name__, repr(reprdict))