{
 "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",
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