support functools.partial as traitlet callback

IPython/utils/traitlets.py

@@ -280,6 +280,86 b' def dlink(source, *targets):'
     """Shorter helper function returning a directional_link object"""
     return directional_link(source, *targets)
 
+
+# Alternative getargspec implementations taken from Sphinx
+if sys.version_info >= (3, 0):
+
+    from functools import partial
+
+    def getargspec(func):
+        """Like inspect.getargspec but supports functools.partial as well."""
+        if inspect.ismethod(func):
+            func = func.__func__
+        if type(func) is partial:
+            orig_func = func.func
+            argspec = getargspec(orig_func)
+            args = list(argspec[0])
+            defaults = list(argspec[3] or ())
+            kwoargs = list(argspec[4])
+            kwodefs = dict(argspec[5] or {})
+            if func.args:
+                args = args[len(func.args):]
+            for arg in func.keywords or ():
+                try:
+                    i = args.index(arg) - len(args)
+                    del args[i]
+                    try:
+                        del defaults[i]
+                    except IndexError:
+                        pass
+                except ValueError:   # must be a kwonly arg
+                    i = kwoargs.index(arg)
+                    del kwoargs[i]
+                    del kwodefs[arg]
+            return inspect.FullArgSpec(args, argspec[1], argspec[2],
+                                       tuple(defaults), kwoargs,
+                                       kwodefs, argspec[6])
+        while hasattr(func, '__wrapped__'):
+            func = func.__wrapped__
+        if not inspect.isfunction(func):
+            raise TypeError('%r is not a Python function' % func)
+        return inspect.getfullargspec(func)
+elif sys.version_info >= (2, 5):
+
+    from functools import partial
+
+    def getargspec(func):
+        """Like inspect.getargspec but supports functools.partial as well."""
+        if inspect.ismethod(func):
+            func = func.im_func
+        parts = 0, ()
+        if type(func) is partial:
+            keywords = func.keywords
+            if keywords is None:
+                keywords = {}
+            parts = len(func.args), keywords.keys()
+            func = func.func
+        if not inspect.isfunction(func):
+            raise TypeError('%r is not a Python function' % func)
+        args, varargs, varkw = inspect.getargs(func.func_code)
+        func_defaults = func.func_defaults
+        if func_defaults is None:
+            func_defaults = []
+        else:
+            func_defaults = list(func_defaults)
+        if parts[0]:
+            args = args[parts[0]:]
+        if parts[1]:
+            for arg in parts[1]:
+                i = args.index(arg) - len(args)
+                del args[i]
+                try:
+                    del func_defaults[i]
+                except IndexError:
+                    pass
+        if sys.version_info >= (2, 6):
+            return inspect.ArgSpec(args, varargs, varkw, func_defaults)
+        else:
+            return (args, varargs, varkw, func_defaults)
+else:
+    getargspec = inspect.getargspec
+
+
 #-----------------------------------------------------------------------------
 # Base TraitType for all traits
 #-----------------------------------------------------------------------------
@@ -570,7 +650,8 b' class HasTraits(py3compat.with_metaclass(MetaHasTraits, object)):'
         for c in callables:
             # Traits catches and logs errors here.  I allow them to raise
             if callable(c):
-                argspec = inspect.getargspec(c)
+                argspec = getargspec(c)
+
                 nargs = len(argspec[0])
                 # Bound methods have an additional 'self' argument
                 # I don't know how to treat unbound methods, but they