PyCourse/函数.ipynb

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2024-06-30 12:03:17 +08:00
{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# 函数"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"函数,实际上是可被调用的完整的程序。它具备输入、处理、输出的功能。\n",
"\n",
"函数包含两个方面:\n",
"\n",
"> * 它的**输入**是怎么构成的(都有哪些参数?如何指定?);\n",
"> * 以及它的**输出**是什么(返回值究竟是什么?)……\n",
"\n",
"```python\n",
"def cow(grass)\n",
" return milk\n",
"```\n",
"\n",
"我们使用函数的过程中,我们常常*有意忽略*它的内部如何完成从输入到输出之间的*处理过程* —— 这就好像我们平日里用灯泡一样,大多数情况下,我们只要知道开关的使用方法就够了 —— 至于为什么按到这个方向上灯会亮,为什么按到另外一个方向上灯会灭,并不是我们作为用户必须关心的事情……\n",
"\n",
"当然,如果你是设计开关的人就不一样了,你必须知道其中的运作原理;但是,最终,你还是希望你的用户用最简单方便的操作界面,而不是必须搞懂所有原理才能够使用你所设计的产品……\n",
"\n",
"当我们用 Python 编程的时候,更多的情况下,我们只不过是在使用别人已经写好的函数."
]
},
{
"cell_type": "markdown",
"metadata": {
"toc-hr-collapsed": true
},
"source": [
"## 示例 print()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### 基本的使用方法"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"它最基本的作用就是把传递给它的值输出到屏幕上,如果不给它任何参数,那么它就输出一个空行:"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"line 1st\n",
"line 2nd\n",
"\n",
"line 4th\n"
]
}
],
"source": [
"print('line 1st')\n",
"print('line 2nd')\n",
"print()\n",
"print('line 4th')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"也可以传递多个参数,参数之间用 `,` 分开,它就会把那些值逐个输出到屏幕,每个值之间默认用空格分开。"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Hello, jack mike ... and all you guys!\n"
]
}
],
"source": [
"print('Hello,', 'jack', 'mike', '...', 'and all you guys!')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"当我们想把变量或者表达式的值插入字符串中的时候,可以用 f-string"
]
},
{
"cell_type": "code",
"execution_count": 12,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Ann is 22 years old.\n"
]
}
],
"source": [
"name = 'Ann'\n",
"age = '22'\n",
"print(f'{name} is {age} years old.')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"但这并不是 `print()` 这个函数的功能,这实际上是 [`f-string`](https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting) 的功能,`f-string` 中用花括号 `{}` 括起来的部分是表达式,最终转换成字符串的时候,那些表达式的值(而不是变量或者表达式本身)会被插入相应的位置……"
]
},
{
"cell_type": "code",
"execution_count": 11,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"'Ann is 22 years old.'"
]
},
"execution_count": 11,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"name = 'Ann'\n",
"age = '22'\n",
"f'{name} is {age} years old.'"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"所以,`print(f'{name} is {age} years old.')` 这一句中,函数 `print()` 完成的还是它最基本的功能:给它什么,它就把什么输出到屏幕上。"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### print() 的官方文档说明"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
"最必须读懂的部分,就是这一行:\n",
"\n",
"> `print(*object, sep=' ', end='\\n', file=sys.stdout, flush=False)` <a href='#fn1' name='fn1b'><sup>[1]</sup></a>\n",
"\n",
"先只注意那些有着 `=` 的参数,`sep=' '`、`end='\\n'`\n",
"\n",
"这其中,先关注这三个 `sep=' '`、`end='\\n'`\n",
"\n",
"> * `sep=' '`:接收多个参数之后,输出时,分隔符号默认为空格,`' '`\n",
"> * `end='\\n'`:输出行的末尾默认是换行符号 `'\\n'`\n",
"\n",
"也就是说,这个函数中有若干个具有默认值的参数,即便我们在调用这个函数的时候,就算没有指定它们,它们也存在于此。\n",
"\n",
"即,当我们调用 `print('Hello', 'world!')` 的时候,相当于我们调用的是 `print('Hello', 'world!', sep=' ', end='\\n', file=sys.stdout, flush=False)`"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Hello world!\n",
"Hello-world!\tHello~world!\n",
"Hello\n",
"world!\n"
]
}
],
"source": [
"print('Hello', 'world!') # 下一行的输出和这一行相同\n",
"print('Hello', 'world!', sep='-', end='\\t')\n",
"print('Hello', 'world!', sep='~') # 上一行的末尾是 \\t所以这一行并没有换行显示\n",
"print('Hello', 'world!', sep='\\n') # 参数之间用换行 \\n 分隔 "
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"> `print()` 这个函数的返回值是 `None` —— 注意,它向屏幕输出的内容,与 `print()` 这个函数的返回值不是一回事。\n",
"\n",
"做为例子,看看 `print(print(1))` 这个语句 —— `print()` 这个函数被调用了两次,第一次是 `print(1)`,它向屏幕输出了一次,完整的输出值实际上是 `str(1) + '\\n'`,而后返回一个值,`None`;而第二次调用 print(),这相当于是向屏幕输出这个 `None`"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n"
]
}
],
"source": [
"print(1)"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"1\n",
"None\n"
]
}
],
"source": [
"print(print(1))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 关键字参数"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"在 Python 中,函数的参数,有两种:\n",
"> * **位置参数**Positional Arguments在官方文档里常被缩写为 *arg*\n",
"> * **关键字参数**Keyword Arguments在官方文档里常被缩写为 *kwarg*\n",
"\n",
"在函数定义中,带有 `=` 的,即,已为其设定了默认值的参数,叫做 Keyword Arguments其它的是 Positional Arguments。\n",
"\n",
"在调用有 Keyword Arguments 的函数之时,如若不提供这些参数,那么参数在执行时,启用的是它在定义的时候为那些 Keyword Arguments 所设定的默认值;如若提供了这些参数的值,那么参数在执行的时候,启用的是接收到的相应值。\n",
"\n",
"比如,`sorted()` 函数,它的定义如下:\n",
"\n",
"> `sorted(iterable, *, key=None, reverse=False)`\n",
"\n",
"现在先只关注它的 Keyword Arguments`reverse`"
]
},
{
"cell_type": "code",
"execution_count": 31,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"['a', 'b', 'c', 'd']"
]
},
"execution_count": 31,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"['d', 'c', 'b', 'a']"
]
},
"execution_count": 31,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"from IPython.core.interactiveshell import InteractiveShell\n",
"InteractiveShell.ast_node_interactivity = \"all\"\n",
"\n",
"sorted('abdc')\n",
"sorted('abdc', reverse=True)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 位置参数"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
"它接收且必须接收两个参数。\n",
"\n",
"> * 当你调用这个函数的时候,括号里写的第一个参数,是被除数,第二个参数是除数 —— 此为该函数的输入;\n",
"> * 而它的返回值是一个元组Tuple至于这是什么东西后面讲清楚其中包括两个值第一个是商第二个是余 —— 此为该函数的输出。"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"(3, 2)"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"3"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"2"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"(0, 3)"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"0"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"3"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"(5, 0)"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"0"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"from IPython.core.interactiveshell import InteractiveShell\n",
"InteractiveShell.ast_node_interactivity = \"all\"\n",
"\n",
"divmod(11, 3)\n",
"a, b = divmod(11, 3)\n",
"a\n",
"b\n",
"\n",
"divmod(3, 11)\n",
"a, b = divmod(3, 11)\n",
"a\n",
"b\n",
"\n",
"tup = divmod(15 , 3)\n",
"tup\n",
"tup[1]"
]
},
{
"cell_type": "markdown",
"metadata": {
"toc-hr-collapsed": false
},
"source": [
"## 可选位置参数"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"有些函数,如 `pow()`,有**可选的位置参数**Optional Positional Arguments。\n",
"\n",
"于是,`pow()` 有两种用法,各有不同的结果:\n",
"\n",
"> * `pow(x, y)` —— 返回值是 `x ** y`\n",
"> * `pow(x, y, z)` —— 返回值是 `x ** y % z`\n",
"\n"
]
},
{
"cell_type": "code",
"execution_count": 40,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"8"
]
},
"execution_count": 40,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"0"
]
},
"execution_count": 40,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"from IPython.core.interactiveshell import InteractiveShell\n",
"InteractiveShell.ast_node_interactivity = \"all\"\n",
"\n",
"pow(2, 3)\n",
"pow(2, 3, 4)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Class 也是函数"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"虽然你现在还不一定知道 Class 究竟是什么,但在阅读官方文档的时候,遇到一些内建函数前面写着 Class比如 `Class bool([x])`,千万别奇怪,因为 Class 本质上来看就是一种特殊类型的函数,也就是说,它也是函数:"
]
},
{
"cell_type": "code",
"execution_count": 44,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"False"
]
},
"execution_count": 44,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"True"
]
},
"execution_count": 44,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"True"
]
},
"execution_count": 44,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"False"
]
},
"execution_count": 44,
"metadata": {},
"output_type": "execute_result"
},
{
"data": {
"text/plain": [
"False"
]
},
"execution_count": 44,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"from IPython.core.interactiveshell import InteractiveShell\n",
"InteractiveShell.ast_node_interactivity = \"all\"\n",
"\n",
"bool()\n",
"bool(3.1415926)\n",
"bool(-3.1415926)\n",
"bool(1 == 2)\n",
"bool(None)"
]
}
],
"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": "3.8.2"
},
"toc-autonumbering": true
},
"nbformat": 4,
"nbformat_minor": 2
}