weakref: Implement atop _weakref primitives.

Signed-off-by: Anson Mansfield <amansfield@mantaro.com>

Author: AJMansfield

python-stdlib/weakref/manifest.py

@@ -0,0 +1,3 @@
+metadata(version="0.0.1")
+
+module("weakref.py")

python-stdlib/weakref/weakref.py

@@ -0,0 +1,54 @@
+import _weakref
+import micropython
+
+
+class _weakref_entry:
+    def __init__(self, parent, obj):
+        self.parent = parent
+
+        if not hasattr(obj, "__dict__") and not hasattr(obj, "__weakref__"):
+            raise TypeError("cannot create weak reference to '{}' object".format(type(obj).__name__))
+        
+        # linked list ensures this will always be part of the same cyclic isolate as the original object
+        self.next = obj
+        try:
+            getattr(obj, "__weakref__").next = self
+        except (KeyError, AttributeError):
+            setattr(obj, "__weakref__", self)
+
+    def __del__(self):
+        p = self.parent
+        p(None)
+        if p.__callback__ is not None:
+            micropython.schedule(p.__callback__, p)
+
+class ref(_weakref.ref):
+    def __init__(self, obj, callback=None):
+        super().__init__(obj)
+        self.__callback__ = callback
+        _weakref_entry(self, obj)
+
+class finalize:
+    def __init__(self, obj, func, *args, **kwargs):
+        self._func = func
+        self._args = args
+        self._kwargs = kwargs
+        self._ref = ref(obj, self)
+
+    @property
+    def alive(self):
+        return self._ref() is not None
+    
+    def peek(self):
+        obj = self._ref()
+        if obj is not None:
+            return (obj, self._func, self._args, self._kwargs)
+    
+    def detach(self):
+        ret = self.peek()
+        self._ref(None)
+        return ret
+    
+    def __call__(self, r=None):
+        return self._func(*self._args, **self._kwargs)
+