Merge pull request #1075 from mila-udem/override_sharedvariablemodifier

Allow override pattern for SharedVariableModifier.

blocks/extensions/training.py

@@ -26,14 +26,38 @@ class SharedVariableModifier(SimpleExtension):
         In the second case, it is a function which takes number of
         iterations done (``int``) and old value of the shared variable
         (with the same dtype as `parameter`).
+    num_args : int, optional
+        The number of arguments to pass to the function. If unspecified,
+        it will be inferred. This is useful if you are using function-like
+        objects for which the arity of the function cannot be inferred.
+
+    Notes
+    -----
+    This class includes a method ``function`` that calls the function
+    passed in the constructor and a ``num_args`` property which computes
+    the number of arguments to use by inspecting the function object.
+    Subclasses may override a method called ``function`` and/or
+    the ``num_args`` property and instead pass ``None`` to the superclass
+    constructor. This can be used to bypass certain serialization issues
+    on Legacy Python regarding the unpicklability of instance
+    method objects.
 
     """
-    def __init__(self, parameter, function, **kwargs):
+    def __init__(self, parameter, function, num_args=None, **kwargs):
         kwargs.setdefault("after_batch", True)
         super(SharedVariableModifier, self).__init__(**kwargs)
         self.parameter = parameter
-        self.function = function
-        self.num_args = len(inspect.getargspec(function).args)
+        self._function = function
+        self._num_args = num_args
+
+    @property
+    def num_args(self):
+        if self._num_args is None:
+            self._num_args = len(inspect.getargspec(self._function).args)
+        return self._num_args
+
+    def function(self, *args):
+        return self._function(*args)
 
     def do(self, which_callback, *args):
         iterations_done = self.main_loop.log.status['iterations_done']