mutable objects as default arguments

rasbt · rasbt · commit e3619125379a · 2014-04-15T16:56:51.000-04:00
diff --git a/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb b/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:7eaf1c17c09445d2807a0560a73437a138201e67de0b44e98b6c853eff059061"
+  "signature": "sha256:6f669267e7ec7d07f6bd0ac72d891bdb4881c22c9396efcc19ca5bff94903cf9"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -44,7 +44,8 @@
       "- [Shallow vs. deep copies if list contains other structures and objects](#shallow_vs_deep)\n",
       "- [Picking True values from and and or expressions](#false_true_expressions)\n",
       "- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
-      "- [Be aware of the consuming generator](#consuming_generator)"
+      "- [Be aware of the consuming generator](#consuming_generator)\n",
+      "- [`bool` is a subclass of `int`](#bool_int)"
      ]
     },
     {
@@ -420,6 +421,13 @@
      ],
      "prompt_number": 9
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "And a fun fact"
+     ]
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -535,6 +543,46 @@
      ],
      "prompt_number": 10
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='bool_int'></a>\n",
+      "\n",
+      "## `bool` is a subclass of `int`\n",
+      "\n",
+      "Chicken or egg? In the history of Python (Python 2.2 to be specific) truth values were implemented via 1 and 0 (similar to the old C), to avoid syntax error in old (but perfectly working) code, `bool` was added as a subclass of `int` in Python 2.3.\n",
+      "\n",
+      "Original source: [http://www.peterbe.com/plog/bool-is-int](http://www.peterbe.com/plog/bool-is-int)"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "print('isinstance(True, int):', isinstance(True, int))\n",
+      "print('True + True:', True + True)\n",
+      "print('3*True:', 3*True)\n",
+      "print('3*True - False:', 3*True - False)\n"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "isinstance(True, int): True\n",
+        "True + True: 2\n",
+        "3*True: 3\n",
+        "3*True - False: 3\n"
+       ]
+      }
+     ],
+     "prompt_number": 16
+    },
     {
      "cell_type": "code",
      "collapsed": false,
diff --git a/not_so_obvious_python_stuff.ipynb b/not_so_obvious_python_stuff.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:7eaf1c17c09445d2807a0560a73437a138201e67de0b44e98b6c853eff059061"
+  "signature": "sha256:6f669267e7ec7d07f6bd0ac72d891bdb4881c22c9396efcc19ca5bff94903cf9"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -44,7 +44,8 @@
       "- [Shallow vs. deep copies if list contains other structures and objects](#shallow_vs_deep)\n",
       "- [Picking True values from and and or expressions](#false_true_expressions)\n",
       "- [Don't use mutable objects as default arguments for functions!](#def_mutable_func)\n",
-      "- [Be aware of the consuming generator](#consuming_generator)"
+      "- [Be aware of the consuming generator](#consuming_generator)\n",
+      "- [`bool` is a subclass of `int`](#bool_int)"
      ]
     },
     {
@@ -420,6 +421,13 @@
      ],
      "prompt_number": 9
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "And a fun fact"
+     ]
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -535,6 +543,46 @@
      ],
      "prompt_number": 10
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='bool_int'></a>\n",
+      "\n",
+      "## `bool` is a subclass of `int`\n",
+      "\n",
+      "Chicken or egg? In the history of Python (Python 2.2 to be specific) truth values were implemented via 1 and 0 (similar to the old C), to avoid syntax error in old (but perfectly working) code, `bool` was added as a subclass of `int` in Python 2.3.\n",
+      "\n",
+      "Original source: [http://www.peterbe.com/plog/bool-is-int](http://www.peterbe.com/plog/bool-is-int)"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "print('isinstance(True, int):', isinstance(True, int))\n",
+      "print('True + True:', True + True)\n",
+      "print('3*True:', 3*True)\n",
+      "print('3*True - False:', 3*True - False)\n"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "isinstance(True, int): True\n",
+        "True + True: 2\n",
+        "3*True: 3\n",
+        "3*True - False: 3\n"
+       ]
+      }
+     ],
+     "prompt_number": 16
+    },
     {
      "cell_type": "code",
      "collapsed": false,
