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diff --git a/basics/python/default_mutable_parameters.ipynb b/basics/python/default_mutable_parameters.ipynb
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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## 1. case 1"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:27:26.778739Z",
+     "start_time": "2022-08-21T01:27:26.765873Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "def add_employee(emp, emp_list = []):\n",
+    "    emp_list.append(emp)\n",
+    "    print(emp_list)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:27:36.118235Z",
+     "start_time": "2022-08-21T01:27:36.113245Z"
+    },
+    "scrolled": true
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "['zhang']\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('zhang')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:27:39.612702Z",
+     "start_time": "2022-08-21T01:27:39.601724Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "['zhang', 'li']\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('li')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:28:01.433747Z",
+     "start_time": "2022-08-21T01:28:01.430249Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "['li']\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('li', [])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:28:15.988491Z",
+     "start_time": "2022-08-21T01:28:15.984261Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "['zhang', 'li', 'li']\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('li')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:30:02.765148Z",
+     "start_time": "2022-08-21T01:30:02.744801Z"
+    }
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(['zhang', 'li', 'li'],)"
+      ]
+     },
+     "execution_count": 12,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "add_employee.__defaults__"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:30:44.627317Z",
+     "start_time": "2022-08-21T01:30:44.623666Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "def add_employee(emp, emp_list = []):\n",
+    "    print(add_employee.__defaults__)\n",
+    "    emp_list.append(emp)\n",
+    "    print(emp_list)\n",
+    "    print(add_employee.__defaults__)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:30:46.009755Z",
+     "start_time": "2022-08-21T01:30:46.002688Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "([],)\n",
+      "['zhang']\n",
+      "(['zhang'],)\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('zhang')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:31:09.233929Z",
+     "start_time": "2022-08-21T01:31:09.230161Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "(['zhang'],)\n",
+      "['zhang', 'li']\n",
+      "(['zhang', 'li'],)\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('li')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 16,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:31:45.175683Z",
+     "start_time": "2022-08-21T01:31:45.172977Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "(['zhang', 'li'],)\n",
+      "['li']\n",
+      "(['zhang', 'li'],)\n"
+     ]
+    }
+   ],
+   "source": [
+    "add_employee('li', [])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:33:18.260279Z",
+     "start_time": "2022-08-21T01:33:18.254488Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "def add_employee_fixed(emp, emp_list = None):\n",
+    "    if emp_list is None:\n",
+    "        emp_list = []\n",
+    "    emp_list.append(emp)\n",
+    "    print(emp_list)\n",
+    "    print(add_employee_fixed.__defaults__)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:33:31.485064Z",
+     "start_time": "2022-08-21T01:33:31.481392Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "(None,)\n",
+      "['zhang']\n",
+      "(None,)\n"
+     ]
+    }
+   ],
+   "source": [
+    "print(add_employee_fixed.__defaults__)\n",
+    "add_employee_fixed('zhang')"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## 2. case 2"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:28:52.580680Z",
+     "start_time": "2022-08-21T01:28:52.576724Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "from datetime import datetime\n",
+    "import time"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:34:32.671514Z",
+     "start_time": "2022-08-21T01:34:32.668551Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "\n",
+    "def print_time(time_to_print=datetime.now()):\n",
+    "    print(time_to_print.strftime('%b %d, %Y %H:%M:%S'))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 23,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:34:48.345468Z",
+     "start_time": "2022-08-21T01:34:48.341096Z"
+    }
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "(datetime.datetime(2022, 8, 21, 9, 34, 32, 669555),)"
+      ]
+     },
+     "execution_count": 23,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "print_time.__defaults__"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:35:35.002020Z",
+     "start_time": "2022-08-21T01:35:34.998605Z"
+    }
+   },
+   "outputs": [],
+   "source": [
+    "\n",
+    "def print_time_fixed(time_to_print=None):\n",
+    "    if time_to_print is None:\n",
+    "        time_to_print = datetime.now()\n",
+    "    print(time_to_print.strftime('%b %d, %Y %H:%M:%S'))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 26,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:35:39.491909Z",
+     "start_time": "2022-08-21T01:35:39.488710Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Aug 21, 2022 09:35:39\n"
+     ]
+    }
+   ],
+   "source": [
+    "print_time_fixed()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 27,
+   "metadata": {
+    "ExecuteTime": {
+     "end_time": "2022-08-21T01:35:43.785204Z",
+     "start_time": "2022-08-21T01:35:43.782140Z"
+    }
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Aug 21, 2022 09:35:43\n"
+     ]
+    }
+   ],
+   "source": [
+    "print_time_fixed()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.6.8"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}