fixes #74

fastcore/dispatch.py

@@ -24,11 +24,20 @@ def anno_ret(func):
 # Cell
 cmp_instance = functools.cmp_to_key(lambda a,b: 0 if a==b else 1 if issubclass(a,b) else -1)
 
+# Cell
+def _chk_defaults(f):
+    try: # Some callables don't have signatures, so ignore those errors
+        params = list(inspect.signature(f).parameters.values())[:2]
+        if any(p.default!=inspect.Parameter.empty for p in params):
+            warn(f"{f.__name__} has default params. These will be ignored.")
+    except ValueError: pass
+
 # Cell
 def _p2_anno(f):
     "Get the 1st 2 annotations of `f`, defaulting to `object`"
     hints = type_hints(f)
     ann = [o for n,o in hints.items() if n!='return']
+    if callable(f): _chk_defaults(f)
     while len(ann)<2: ann.append(object)
     return ann[:2]
 
@@ -72,7 +81,6 @@ def __init__(self, funcs=(), bases=()):
 
     def add(self, f):
         "Add type `t` and function `f`"
-        if f and getattr(f,'__defaults__',None): warn(f"{f.__name__} has default params. These will be ignored.")
         a0,a1 = _p2_anno(f)
         t = self.funcs.d.get(a0)
         if t is None:

nbs/03_dispatch.ipynb

@@ -210,6 +210,21 @@
     "test_eq(sorted(td, key=cmp_instance), [numbers.Number, numbers.Integral, int])"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "#export\n",
+    "def _chk_defaults(f):\n",
+    "    try: # Some callables don't have signatures, so ignore those errors\n",
+    "        params = list(inspect.signature(f).parameters.values())[:2]\n",
+    "        if any(p.default!=inspect.Parameter.empty for p in params):\n",
+    "            warn(f\"{f.__name__} has default params. These will be ignored.\")\n",
+    "    except ValueError: pass"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -221,6 +236,7 @@
     "    \"Get the 1st 2 annotations of `f`, defaulting to `object`\"\n",
     "    hints = type_hints(f)\n",
     "    ann = [o for n,o in hints.items() if n!='return']\n",
+    "    if callable(f): _chk_defaults(f)\n",
     "    while len(ann)<2: ann.append(object)\n",
     "    return ann[:2]"
    ]
@@ -248,7 +264,19 @@
     "test_eq(_p2_anno(_f), (int,int))\n",
     "def _f(a:int, b:str)->float: pass\n",
     "test_eq(_p2_anno(_f), (int,str))\n",
-    "test_eq(_p2_anno(attrgetter('foo')), (object,object))"
+    "test_eq(_p2_anno(attrgetter('foo')), (object,object))\n",
+    "_p2_anno(None)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "#hide\n",
+    "def _f(x:int,y:int=10): pass\n",
+    "test_warns(lambda: _p2_anno(_f))"
    ]
   },
   {
@@ -336,7 +364,6 @@
     "\n",
     "    def add(self, f):\n",
     "        \"Add type `t` and function `f`\"\n",
-    "        if f and getattr(f,'__defaults__',None): warn(f\"{f.__name__} has default params. These will be ignored.\")\n",
     "        a0,a1 = _p2_anno(f)\n",
     "        t = self.funcs.d.get(a0)\n",
     "        if t is None:\n",
@@ -1083,6 +1110,15 @@
     "test_eq(f_td_test('a','b'), 'ab')"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "test_warns??"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -1103,6 +1139,45 @@
     "test_warns(outer,True)"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "/home/jhoward/anaconda3/lib/python3.7/site-packages/ipykernel_launcher.py:12: UserWarning: _test has default params. These will be ignored.\n",
+      "  if sys.path[0] == '':\n"
+     ]
+    }
+   ],
+   "source": [
+    "@typedispatch\n",
+    "def _test(x:int,y:int,z=10): return x*y*10"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "60"
+      ]
+     },
+     "execution_count": null,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "_test(3,2)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},