anfedorov · June 18, 2009 09:42 · Jun 18, 2009
diff --git a/decorations.py b/decorations.py
@@ -0,0 +1,77 @@
+from functools import wraps, partial
+from inspect import getargspec
+
+def _param_update(old_params, new_params):
+    args, kwargs = old_params
+
+    if type(new_params) == tuple:
+        if len(new_params) == 2 and type(new_params[0]) == tuple and type(new_params[1]) == dict:
+            args = new_params[0]
+            kwargs.update(new_params[1])
+        else:
+            args = new_params
+    elif type(new_params) == dict:
+        kwargs.update(new_params)
+
+    return (args, kwargs)
+
+def filter_dict(d, fltr):
+    return dict( (x, d[x]) for x in fltr if x in d )
+
+def apply_some(f, *args, **kwargs):
+    fspec = getargspec(f)
+    return f(*args, **kwargs) if fspec.keywords else f( *args, **filter_dict(kwargs, fspec.args) ) 
+
+def _metadecorator(decoration, params="maybe"):
+    "Takes a decoration to pre-apply to a decoratee"
+    def cap_params(*dec_params, **dec_kwargs):
+        "Captures decoration parameters"
+        @wraps(decoration)
+        def decorator(decoratee):
+            "The decorator - takes a decoratee to decorate"
+            @wraps(decoratee)
+            def decorated(*args, **kwargs):
+                "The decorated decoratee"
+                # the decoration will be passed the decoratee and (optionally) two sets of arguments
+                return apply_some(decoration, decoratee, args=args, kwargs=kwargs, dec_params=dec_params, dec_kwargs=dec_kwargs)
+            return decorated
+
+        if params=="maybe" and not dec_kwargs and len(dec_params)==1 and callable(dec_params[0]):
+            decoratee = dec_params[0]
+            dec_params = ()
+            return decorator(decoratee)
+        else:
+            return decorator
+
+    return cap_params
+
+def decoration(decoration=None, has_params="maybe"):
+    "Meta-decorates"
+    if decoration:
+        dec_args = getargspec(decoration).args
+        if 'dec_params' in dec_args or 'dec_kwargs' in dec_args:
+            return _metadecorator(decoration, params=has_params)
+        else:
+            return _metadecorator(decoration, params=has_params)()
+    else:
+        return partial(decoration, params=has_params)
+
+@decoration
+def predecoration(f, args, kwargs):
+    "Declares something as a predecoration"
+    def predecorator(g, **kwds):
+        # at this point, `f` will be our predecoration and `g` will be our decoratee.
+        update = apply_some(f, g, **kwds)
+        gargs, gkwargs = _param_update((kwds['args'], kwds['kwargs']), update)
+        return g(*gargs, **gkwargs)
+    return _metadecorator(predecorator)(*args, **kwargs)
+
+@decoration
+def postdecoration(f, args, kwargs, dec_kwargs):
+    "Declares something as a postdecoration"
+    def postdecorator(g, **kwds):
+        # at this point, `f` will be our postdecoration and `g` will be our decoratee.
+        res = g(*kwds['args'], **kwds['kwargs'])
+        return apply_some(f, res, *kwds['dec_params'], **kwds['dec_kwargs'])
+    return _metadecorator(postdecorator, dec_kwargs.get('has_params', 'maybe'))(*args, **kwargs)
+