sorted_topologically function instead of sorted to fix issue #100

Author: kessido

fastcore/_nbdev.py

@@ -125,7 +125,7 @@
          "parallel_gen": "02_utils.ipynb",
          "type_hints": "03_dispatch.ipynb",
          "anno_ret": "03_dispatch.ipynb",
-         "cmp_instance": "03_dispatch.ipynb",
+         "sorted_topologically": "03_dispatch.ipynb",
          "TypeDispatch": "03_dispatch.ipynb",
          "DispatchReg": "03_dispatch.ipynb",
          "typedispatch": "03_dispatch.ipynb",

fastcore/dispatch.py

@@ -1,6 +1,6 @@
 # AUTOGENERATED! DO NOT EDIT! File to edit: nbs/03_dispatch.ipynb (unless otherwise specified).
 
-__all__ = ['type_hints', 'anno_ret', 'cmp_instance', 'TypeDispatch', 'DispatchReg', 'typedispatch', 'cast',
+__all__ = ['type_hints', 'anno_ret', 'sorted_topologically', 'TypeDispatch', 'DispatchReg', 'typedispatch', 'cast',
            'retain_meta', 'default_set_meta', 'retain_type', 'retain_types', 'explode_types']
 
 # Cell
@@ -23,7 +23,13 @@ def anno_ret(func):
     return ann.get('return')
 
 # Cell
-cmp_instance = functools.cmp_to_key(lambda a,b: 0 if a==b else 1 if issubclass(a,b) else -1)
+def sorted_topologically(iterable, *, cmp=operator.lt, reverse=False):
+    "Return a new list containing all items from the iterable sorted topologically"
+    l,res = L(list(iterable)),[]
+    for _ in range(len(l)):
+        t = l.reduce(lambda x,y: y if cmp(x,y) else x)
+        res.append(t), l.remove(t)
+    return res[::-1] if reverse else res
 
 # Cell
 def _chk_defaults(f, ann):
@@ -49,7 +55,7 @@ class _TypeDict:
     def __init__(self): self.d,self.cache = {},{}
 
     def _reset(self):
-        self.d = {k:self.d[k] for k in sorted(self.d, key=cmp_instance, reverse=True)}
+        self.d = {k:self.d[k] for k in sorted_topologically(self.d, cmp=issubclass, reverse=True)}
         self.cache = {}
 
     def add(self, t, f):

nbs/03_dispatch.ipynb

@@ -25,7 +25,9 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "tags": []
+   },
    "outputs": [],
    "source": [
     "from nbdev.showdoc import *\n",
@@ -199,7 +201,13 @@
    "outputs": [],
    "source": [
     "#export\n",
-    "cmp_instance = functools.cmp_to_key(lambda a,b: 0 if a==b else 1 if issubclass(a,b) else -1)"
+    "def sorted_topologically(iterable, *, cmp=operator.lt, reverse=False):\n",
+    "    \"Return a new list containing all items from the iterable sorted topologically\"\n",
+    "    l,res = L(list(iterable)),[]\n",
+    "    for _ in range(len(l)):\n",
+    "        t = l.reduce(lambda x,y: y if cmp(x,y) else x)\n",
+    "        res.append(t), l.remove(t)\n",
+    "    return res[::-1] if reverse else res"
    ]
   },
   {
@@ -209,7 +217,18 @@
    "outputs": [],
    "source": [
     "td = {int:1, numbers.Number:2, numbers.Integral:3}\n",
-    "test_eq(sorted(td, key=cmp_instance), [numbers.Number, numbers.Integral, int])"
+    "test_eq(sorted_topologically(td, cmp=issubclass), [numbers.Number, numbers.Integral, int])\n",
+    "test_eq(sorted_topologically(td, cmp=issubclass, reverse=True), [int, numbers.Integral, numbers.Number])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "td = sorted_topologically([numbers.Integral, tuple, list, int, dict], cmp=issubclass)\n",
+    "assert td.index(numbers.Integral) < td.index(int)"
    ]
   },
   {
@@ -339,7 +358,7 @@
     "    def __init__(self): self.d,self.cache = {},{}\n",
     "\n",
     "    def _reset(self):\n",
-    "        self.d = {k:self.d[k] for k in sorted(self.d, key=cmp_instance, reverse=True)}\n",
+    "        self.d = {k:self.d[k] for k in sorted_topologically(self.d, cmp=issubclass, reverse=True)}\n",
     "        self.cache = {}\n",
     "\n",
     "    def add(self, t, f):\n",