collections.defaultdict: Add implementation.

In a namespace package.

collections.defaultdict/collections/defaultdict.py

@@ -0,0 +1,24 @@
+class defaultdict:
+
+    def __init__(self, default_factory=None, **kwargs):
+        self.d = kwargs
+        self.default_factory = default_factory
+
+    def __getitem__(self, key):
+        try:
+            return self.d[key]
+        except KeyError:
+            if self.default_factory is None:
+                raise
+            v = self.__missing__(key)
+            self.d[key] = v
+            return v
+
+    def __setitem__(self, key, v):
+        self.d[key] = v
+
+    def __delitem__(self, key):
+        del self.d[key]
+
+    def __missing__(self, key):
+        return self.default_factory()

collections.defaultdict/setup.py

@@ -0,0 +1,10 @@
+from distutils.core import setup
+
+setup(name='micropython-collections.defaultdict',
+      version='0.1',
+      description='collections.defaultdict module for MicroPython',
+      url='https://github.com/micropython/micropython/issues/405',
+      author='Paul Sokolovsky',
+      author_email='micro-python@googlegroups.com',
+      license='MIT',
+      packages=['collections'])

collections.defaultdict/test_defaultdict.py

@@ -0,0 +1,8 @@
+from collections import defaultdict
+
+d = defaultdict(lambda:42)
+assert d[1] == 42
+d[2] = 3
+assert d[2] == 3
+del d[1]
+assert d[1] == 42