PyLzuCSEdu/1 函数的参数.ipynb

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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 函数的参数\n",
    "\n",
    "## 一、基础知识"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Python 没有函数重载"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def ff( x ): return x   \n",
    "def ff( x,y ): return x + y   # 同名函数后面的遮挡前面函数\n",
    "\n",
    "ff(2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### 值传递和引用传递"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 值传递 :字符串、数字、元组 [ 不可变 ]\n",
    "\n",
    "def ff(x):  x += 1   # 不改变调用值 a\n",
    "a = 5 ; ff(a) ; a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 引用传递: 列表、字典 [可变]\n",
    "\n",
    "def ff(x): x.append(1)  # 改变调用值 a\n",
    "a = [ 0 ] ; ff(a); a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 二、函数参数形式\n",
    "\n",
    "Python函数的参数传递非常灵活，支持多种参数形式，使得函数定义和调用更加强大和灵活。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.1 普通参数"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 位置参数\n",
    "\n",
    "位置参数是最基本的参数形式，按照它们在函数定义中的顺序传递。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello Alice, you are 25 years old\n"
     ]
    }
   ],
   "source": [
    "def greet(name, age):  # name 和 age 是位置参数\n",
    "    print(f\"Hello {name}, you are {age} years old\")\n",
    "\n",
    "# 调用方式\n",
    "greet(\"Alice\", 25)  # 参数按照定义的顺序传入,\"Alice\" 对应 name，30 对应 age"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 默认参数\n",
    "\n",
    "为某些参数设置默认值，如果调用时不提供该参数，则使用默认值。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello, Bob. You are 18 years old.\n",
      "Hello, Charlie. You are 25 years old.\n"
     ]
    }
   ],
   "source": [
    "def greet(name, age=18):\n",
    "    print(f\"Hello, {name}. You are {age} years old.\")\n",
    "\n",
    "greet(\"Bob\")          # 使用默认年龄\n",
    "greet(\"Charlie\", 25)  # 提供具体年龄"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 调用函数时指定参数名\n",
    "\n",
    "通过参数名进行传递，参数顺序可以任意调整，提高了代码的可读性。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 50,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Charlie 20\n",
      "Charlie 20\n",
      "Charlie 20\n",
      "Charlie 20\n"
     ]
    }
   ],
   "source": [
    "def greet( name,age ): print( name,age)    \n",
    "\n",
    "greet( name = 'Charlie', age=20 )  # 命名传递参数,更清楚\n",
    "greet( age = 20,name = 'Charlie' )  # 顺序可以改变\n",
    "greet( 'Charlie',age = 20 )   # 混合使用,普通调用放前面,命名调用放后面\n",
    "\n",
    "name,age = 'Charlie',20  \n",
    "greet( name = name, age = age ) # 形参、实参数同名的情况"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.2 可变参数"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 可变位置参数 \n",
    "- 使用星号（*）定义可变数量的位置参数，这些参数被存储在一个元组中。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6\n",
      "15\n"
     ]
    }
   ],
   "source": [
    "def sum_numbers(*args):\n",
    "    return sum(args)\n",
    "\n",
    "# 调用方式\n",
    "print(sum_numbers(1, 2, 3))       # 输出: 6\n",
    "print(sum_numbers(1, 2, 3, 4, 5)) # 输出: 15"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 关键字参数（命名参数、字典参数）\n",
    "\n",
    "- 放在可变位置参数后面 \n",
    "- 调用的时候，必须使用名字赋值形式"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(1, (2, 3), 2)"
      ]
     },
     "execution_count": 51,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def ff(a,*b,c): return a,b,c\n",
    "\n",
    "ff( 1,c = 2 )  \n",
    "ff( 1,2,c = 2 )\n",
    "ff( 1,2,3,c = 2 ) "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 没有可变参数，也要用 * 占位\n",
    "\n",
    "def ff(a,*,b): return a,b\n",
    "ff(1,b=2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 () 0\n",
      "1 2\n",
      "1 3\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "(None, None)"
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     "execution_count": 52,
     "metadata": {},
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   ],
   "source": [
    "# 有默认值的情况\n",
    "\n",
    "def ff( a,*b,c = 0 ): print(a,b,c)  \n",
    "ff(1)\n",
    "\n",
    "def ff( a = 1,*, b = 2 ): print(a,b)     \n",
    "ff(),ff( b = 3 )    # 前面是带默认值的位置参数"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 53,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello Alice, you are 25 years old\n"
     ]
    }
   ],
   "source": [
    "# 函数以空*开头，强制函数用关键字参数，可提升代码可读性\n",
    "\n",
    "def greet(*, name, age):    # * 之后的参数只能用关键字参数\n",
    "    print(f\"Hello {name}, you are {age} years old\")\n",
    "\n",
    "# 正确调用\n",
    "greet(name=\"Alice\", age=25)\n",
    "\n",
    "# 错误调用\n",
    "# greet(\"Alice\", 25)    # 无 关键字命名 错误"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 可变关键字参数\n",
    "\n",
    "使用两个星号（**）定义可变数量的关键字参数。这些参数被存储在一个字典中。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "name: Eve\n",
      "age: 28\n",
      "city: London\n"
     ]
    }
   ],
   "source": [
    "def print_info(**kwargs):\n",
    "    for key, value in kwargs.items():\n",
    "        print(f\"{key}: {value}\")\n",
    "\n",
    "# 调用方式\n",
    "print_info( name=\"Eve\", age=28, city=\"London\" )"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 解包可变参数\n",
    "\n",
    "在函数调用时，可以使用星号（*）或两个星号（**）来解包列表、元组或字典，将其中的元素或键值对作为参数传递给函数。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def func(a, b, *args, **kwargs):\n",
    "    print(a, b, args)\n",
    "    for key, value in kwargs.items():\n",
    "        print(key, value)\n",
    "\n",
    "args = (3, 4)  # 或者 [\"Alice\", 25, \"Beijing\"] 其它序列容器\n",
    "kwargs = {'x': 5, 'y': 6}        \n",
    "func(1, 2, *args, **kwargs)  "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.3 混合使用各种参数"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 () 2 {}\n",
      "1 () 2 {'d': 3}\n",
      "1 () 2 {'d': 3, 'e': 4}\n",
      "1 () 2 {'d': 3, 'e': 4}\n",
      "1 () 2 {'d': 3, 'e': 4}\n"
     ]
    }
   ],
   "source": [
    "# 顺序：普通参数、可变位置参数、命名参数、可变关键字参数\n",
    "# 可变位置参数后面，命名参数选取剩下的就是可变关键字参数\n",
    "\n",
    "def ff( a,*b,c,**d ): print( a,b,c,d )\n",
    "\n",
    "ff( 1,c=2 )\n",
    "ff( 1,c=2,d=3 )\n",
    "ff( 1,c=2,d=3,e=4 )\n",
    "ff( 1,d=3,e=4,c=2 )\n",
    "ff( 1,d=3,c=2,e=4 )  # 可推测其参数确定机制"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 55,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "普通参数 name : 1\n",
      "普通参数 age : 2\n",
      "可变参数 args : (3,)\n",
      "命名参数 department : math\n",
      "字典参数 kwargs : {}\n"
     ]
    }
   ],
   "source": [
    "def ff( name , age ='20', *args, department = 'cs', **kwargs ): \n",
    "    '''\n",
    "        name 是必需的位置参数。\n",
    "        age 是带有默认值的位置参数。\n",
    "        *args 收集额外的位置参数。\n",
    "        **kwargs 收集额外的关键字参数。\n",
    "    '''    \n",
    "    print('普通参数 name :', name )\n",
    "    print('普通参数 age :', age )\n",
    "    print('可变参数 args :', args )\n",
    "    print('命名参数 department :', department )\n",
    "    print('字典参数 kwargs :', kwargs )\n",
    "\n",
    "# ff()\n",
    "# ff(1)\n",
    "# ff(1,2)\n",
    "# ff(1,2,3)\n",
    "# ff(1,2,3,4)\n",
    "# ff(1,2,3,department='math')\n",
    "# ff(1,2,3,u1='math')\n",
    "# ff(1,2,3,4,5,u1='tsg',department='cmu',u2='pku' )"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 基础代码中常用( *args,**kwargs )参数表来抽象表示一般函数的参数\n",
    "\n",
    "def ff( *args,**kwargs ): \n",
    "    pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 总结\n",
    "\n",
    "#### 参数顺序规则\n",
    "<code>\n",
    "def function(\n",
    "    位置参数,           # 普通参数\n",
    "    默认参数 = '默认值',     # 默认参数\n",
    "    *args,            # 可变位置参数    \n",
    "    关键字参数,       # 普通关键字参数\n",
    "    **kwargs          # 可变关键字参数\n",
    "): pass\n",
    "</code>    \n",
    "\n",
    "- 可以有默认值：普通位置参数、 关键字参数"
   ]
  }
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