chore: ch2 note - assignment expression

chchchuang · chchchuang · commit b3cb4b0575e8 · 2025-07-27T00:51:08.000+08:00
diff --git a/02-array-seq/array-seq.ipynb b/02-array-seq/array-seq.ipynb
@@ -114,7 +114,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 5,
    "metadata": {},
    "outputs": [
     {
@@ -123,7 +123,7 @@
        "[36, 162, 163, 165, 8364, 164]"
       ]
      },
-     "execution_count": 2,
+     "execution_count": 5,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -145,7 +145,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 6,
    "metadata": {},
    "outputs": [
     {
@@ -154,7 +154,7 @@
        "'ABC'"
       ]
      },
-     "execution_count": 3,
+     "execution_count": 6,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -167,7 +167,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 7,
    "metadata": {},
    "outputs": [
     {
@@ -176,7 +176,7 @@
        "[65, 66, 67]"
       ]
      },
-     "execution_count": 4,
+     "execution_count": 7,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -185,9 +185,21 @@
     "codes"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "`:=` 允許你在一個運算式中給變數賦值，且 scope 是封閉的函式 (enclosing function)，所以在 listcomp 完成後還可以讀取。例如：\n",
+    "```python\n",
+    "if (n := len(data)) > 10:\n",
+    "    print(f\"Data is too long: {n}\")\n",
+    "```\n",
+    "這樣就不需要重複 `len(data)` 兩次。"
+   ]
+  },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 8,
    "metadata": {
     "collapsed": false,
     "pycharm": {
@@ -201,7 +213,7 @@
        "67"
       ]
      },
-     "execution_count": 5,
+     "execution_count": 8,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -211,6 +223,30 @@
     "last"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "inside demo: 6\n",
+      "global total: 0\n"
+     ]
+    }
+   ],
+   "source": [
+    "def demo(data, total):\n",
+    "    _ = [total := total + v for v in data]\n",
+    "    print(\"inside demo:\", total)\n",
+    "\n",
+    "total = 0\n",
+    "demo([1,2,3], 0)\n",
+    "print(\"global total:\", total)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
