From 80fa7c64c3d403742e1f7041da4a345b58075635 Mon Sep 17 00:00:00 2001 From: jaywcjlove <398188662@qq.com> Date: Wed, 2 Nov 2022 16:06:48 +0800 Subject: [PATCH] feat: add `python.md` cheatsheet (#13). --- README.md | 1 + docs/python.md | 1225 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 1226 insertions(+) create mode 100644 docs/python.md diff --git a/README.md b/README.md index c6b6138..5c47e23 100644 --- a/README.md +++ b/README.md @@ -27,6 +27,7 @@ Quick Reference [Java](./docs/java.md) [Markdown](./docs/markdown.md) [MySQL](./docs/mysql.md) +[Python](./docs/python.md) [Swift](./docs/swift.md) [SwiftUI](./docs/swiftui.md) [TOML](./docs/toml.md) diff --git a/docs/python.md b/docs/python.md new file mode 100644 index 0000000..748d4c3 --- /dev/null +++ b/docs/python.md @@ -0,0 +1,1225 @@ +Python 3 备忘清单 +=== + +Python 备忘单是 [Python 3](https://www.python.org/) 编程语言的单页参考表 + +入门 +----- + +### 介绍 + +- [Python](https://www.python.org/) _(python.org)_ +- [Learn X in Y minutes](https://learnxinyminutes.com/docs/python/) _(learnxinyminutes.com)_ +- [Regex in python](./regex.md#python-中的正则表达式) _(quickref.me)_ + +### Hello World + +```python +>>> print("Hello, World!") +Hello, World! +``` + +Python 中著名的“Hello World”程序 + +### 变量 + +```python +age = 18 # 年龄是 int 类型 +name = "John" # name 现在是 str 类型 +print(name) +``` + +Python 不能在没有赋值的情况下声明变量 + +### 数据类型 + + +:-| :- +:-| :- +`str` | Text +`int`, `float`, `complex` | Numeric +`list`, `tuple`, `range` | Sequence +`dict` | Mapping +`set`, `frozenset` | Set +`bool` | Boolean +`bytes`, `bytearray`, `memoryview` | Binary + +查看: [Data Types](#python-数据类型) + +### Slicing String + +```python +>>> msg = "Hello, World!" +>>> print(msg[2:5]) +llo +``` + +查看: [Strings](#python-字符串) + +### Lists +```python +mylist = [] +mylist.append(1) +mylist.append(2) +for item in mylist: + print(item) # 打印输出 1,2 +``` + +查看: [Lists](#python-lists) + + +### If Else + +```python +num = 200 +if num > 0: + print("num is greater than 0") +else: + print("num is not greater than 0") +``` +查看: [流程控制](#python-流程控制) + +### 循环 + +```python +for item in range(6): + if item == 3: break + print(item) +else: + print("Finally finished!") +``` +查看: [Loops](#python-循环) + + +### 函数 + +```python +>>> def my_function(): +... print("来自函数的你好") +... +>>> my_function() +来自函数的你好 +``` + +查看: [Functions](#python-functions) + +### 文件处理 + + +```python +with open("myfile.txt", "r", encoding='utf8') as file: + for line in file: + print(line) +``` + +查看: [文件处理](#python-文件处理) + +### 算术 + +```python +result = 10 + 30 # => 40 +result = 40 - 10 # => 30 +result = 50 * 5 # => 250 +result = 16 / 4 # => 4.0 (Float Division) +result = 16 // 4 # => 4 (Integer Division) +result = 25 % 2 # => 1 +result = 5 ** 3 # => 125 +``` + +`/` 表示 x 和 y 的商，`//` 表示 x 和 y 的底商，另见 [StackOverflow](https://stackoverflow.com/a/183870/13192320) + +### 加等于 + +```python +counter = 0 +counter += 10 # => 10 +counter = 0 +counter = counter + 10 # => 10 +message = "Part 1." +# => Part 1.Part 2. +message += "Part 2." +``` + +### f-字符串(Python 3.6+) + +```python +>>> website = 'Quickref.ME' +>>> f"Hello, {website}" +"Hello, Quickref.ME" +>>> num = 10 +>>> f'{num} + 10 = {num + 10}' +'10 + 10 = 20' +``` + +查看: [Python F-Strings](#python-f-strings-since-python) + +Python 数据类型 +--------------- + +### 字符串 + +```python +hello = "Hello World" +hello = 'Hello World' +multi_string = """Multiline Strings +Lorem ipsum dolor sit amet, +consectetur adipiscing elit """ +``` +查看: [Strings](#python-字符串) + +### 数字 + +```python +x = 1 # int +y = 2.8 # float +z = 1j # complex +>>> print(type(x)) + +``` + +### 布尔值 + +```python +my_bool = True +my_bool = False +bool(0) # => False +bool(1) # => True +``` + +### Lists + +```python +list1 = ["apple", "banana", "cherry"] +list2 = [True, False, False] +list3 = [1, 5, 7, 9, 3] +list4 = list((1, 5, 7, 9, 3)) +``` +查看: [Lists](#python-lists) + + +### 元组 Tuple + +```python +my_tuple = (1, 2, 3) +my_tuple = tuple((1, 2, 3)) +``` + +类似于 List 但不可变 + +### Set + +```python +set1 = {"a", "b", "c"} +set2 = set(("a", "b", "c")) +``` + +一组独特的项目/对象 + +### 字典 Dictionary + +```python +>>> empty_dict = {} +>>> a = {"one": 1, "two": 2, "three": 3} +>>> a["one"] +1 +>>> a.keys() +dict_keys(['one', 'two', 'three']) +>>> a.values() +dict_values([1, 2, 3]) +>>> a.update({"four": 4}) +>>> a.keys() +dict_keys(['one', 'two', 'three', 'four']) +>>> a['four'] +4 +``` + +Key：值对，JSON 类对象 + +### Casting + +#### 整数 Integers + +```python +x = int(1) # x 将是 1 +y = int(2.8) # y 将是 2 +z = int("3") # z 将是 3 +``` + +#### 浮点数 Floats + +```python +x = float(1) # x 将为 1.0 +y = float(2.8) # y 将是 2.8 +z = float("3") # z 将为 3.0 +w = float("4.2") # w 将是 4.2 +``` + +#### 字符串 Strings + +```python +x = str("s1") # x 将是 's1' +y = str(2) # y 将是 '2' +z = str(3.0) # z 将是 '3.0' +``` + +Python 字符串 +------------ + +### 类数组 + +```python +>>> hello = "Hello, World" +>>> print(hello[1]) +e +>>> print(hello[-1]) +d +``` + +获取位置 `1` 或最后的字符 + +### 循环 + +```python +>>> for char in "foo": +... print(char) +f +o +o +``` + +遍历单词 `foo` 中的字母 + +### 切片字符串 + + +```java + ┌───┬───┬───┬───┬───┬───┬───┐ + | m | y | b | a | c | o | n | + └───┴───┴───┴───┴───┴───┴───┘ + 0 1 2 3 4 5 6 7 +-7 -6 -5 -4 -3 -2 -1 +``` + +--- + +```python +>>> s = 'mybacon' +>>> s[2:5] +'bac' +>>> s[0:2] +'my' +``` + +--- + +```python +>>> s = 'mybacon' +>>> s[:2] +'my' +>>> s[2:] +'bacon' +>>> s[:2] + s[2:] +'mybacon' +>>> s[:] +'mybacon' +``` + +--- + +```python +>>> s = 'mybacon' +>>> s[-5:-1] +'baco' +>>> s[2:6] +'baco' +``` + +#### 迈着大步 + +```python +>>> s = '12345' * 5 +>>> s +'1234512345123451234512345' +>>> s[::5] +'11111' +>>> s[4::5] +'55555' +>>> s[::-5] +'55555' +>>> s[::-1] +'5432154321543215432154321' +``` + +### 字符串长度 + +```python +>>> hello = "Hello, World!" +>>> print(len(hello)) +13 +``` + +`len()` 函数返回字符串的长度 + +### 多份 +```python +>>> s = '===+' +>>> n = 8 +>>> s * n +'===+===+===+===+===+===+===+===+' +``` + +### 检查字符串 + +```python +>>> s = 'spam' +>>> s in 'I saw spamalot!' +True +>>> s not in 'I saw The Holy Grail!' +True +``` + +### 连接 + +```python +>>> s = 'spam' +>>> t = 'egg' +>>> s + t +'spamegg' +>>> 'spam' 'egg' +'spamegg' +``` + +### 格式化 + + +```python +name = "John" +print("Hello, %s!" % name) +``` +--- +```python +name = "John" +age = 23 +print("%s is %d years old." % (name, age)) +``` + +#### format() 方法 + +```python +txt1 = "My name is {fname}, I'm {age}".format(fname="John", age=36) +txt2 = "My name is {0}, I'm {1}".format("John", 36) +txt3 = "My name is {}, I'm {}".format("John", 36) +``` + +### Input 输入 + +```python +>>> name = input("Enter your name: ") +Enter your name: Tom +>>> name +'Tom' +``` + +从控制台获取输入数据 + +### Join 加入 + +```python +>>> "#".join(["John", "Peter", "Vicky"]) +'John#Peter#Vicky' +``` + +### Endswith 以..结束 + +```python +>>> "Hello, world!".endswith("!") +True +``` + +Python F 字符串（自 Python 3.6+ 起） +---------------- + +### f-Strings 用法 + + +```python +>>> website = 'Reference' +>>> f"Hello, {website}" +"Hello, Reference" +>>> num = 10 +>>> f'{num} + 10 = {num + 10}' +'10 + 10 = 20' +>>> f"""He said {"I'm John"}""" +"He said I'm John" +>>> f'5 {"{stars}"}' +'5 {stars}' +>>> f'{{5}} {"stars"}' +'{5} stars' +>>> name = 'Eric' +>>> age = 27 +>>> f"""Hello! +... I'm {name}. +... I'm {age}.""" +"Hello!\n I'm Eric.\n I'm 27." +``` + +它从 Python 3.6 开始可用，另见: [格式化的字符串文字](https://docs.python.org/3/reference/lexical_analysis.html#f-strings) + +### f-Strings 填充对齐 + +```python +>>> f'{"text":10}' # [宽度] +'text ' +>>> f'{"test":*>10}' # 向左填充 +'******test' +>>> f'{"test":*<10}' # 填写正确 +'test******' +>>> f'{"test":*^10}' # 填充中心 +'***test***' +>>> f'{12345:0>10}' # 填写数字 +'0000012345' +``` + +### f-Strings 类型 + + +```python +>>> f'{10:b}' # binary 二进制类型 +'1010' +>>> f'{10:o}' # octal 八进制类型 +'12' +>>> f'{200:x}' # hexadecimal 十六进制类型 +'c8' +>>> f'{200:X}' +'C8' +>>> f'{345600000000:e}' # 科学计数法 +'3.456000e+11' +>>> f'{65:c}' # 字符类型 +'A' +>>> f'{10:#b}' # [类型] 带符号（基础） +'0b1010' +>>> f'{10:#o}' +'0o12' +>>> f'{10:#x}' +'0xa' +``` + +### F-Strings Sign + +```python +>>> f'{12345:+}' # [sign] (+/-) +'+12345' +>>> f'{-12345:+}' +'-12345' +>>> f'{-12345:+10}' +' -12345' +>>> f'{-12345:+010}' +'-000012345' +``` + +### F-Strings 其它 + +```python +>>> f'{-12345:0=10}' # 负数 +'-000012345' +>>> f'{12345:010}' # [0] 快捷方式（不对齐） +'0000012345' +>>> f'{-12345:010}' +'-000012345' +>>> import math # [.precision] +>>> math.pi +3.141592653589793 +>>> f'{math.pi:.2f}' +'3.14' +>>> f'{1000000:,.2f}' # [分组选项] +'1,000,000.00' +>>> f'{1000000:_.2f}' +'1_000_000.00' +>>> f'{0.25:0%}' # 百分比 +'25.000000%' +>>> f'{0.25:.0%}' +'25%' +``` + +Python Lists +------------ + +### 定义 + +```python +>>> li1 = [] +>>> li1 +[] +>>> li2 = [4, 5, 6] +>>> li2 +[4, 5, 6] +>>> li3 = list((1, 2, 3)) +>>> li3 +[1, 2, 3] +>>> li4 = list(range(1, 11)) +>>> li4 +[1, 2, 3, 4, 5, 6, 7, 8, 9, 10] +``` + +### 生成 + + +```python +>>> list(filter(lambda x : x % 2 == 1, range(1, 20))) +[1, 3, 5, 7, 9, 11, 13, 15, 17, 19] +>>> [x ** 2 for x in range (1, 11) if x % 2 == 1] +[1, 9, 25, 49, 81] +>>> [x for x in [3, 4, 5, 6, 7] if x > 5] +[6, 7] +>>> list(filter(lambda x: x > 5, [3, 4, 5, 6, 7])) +[6, 7] +``` + +### 添加 + +```python +>>> li = [] +>>> li.append(1) +>>> li +[1] +>>> li.append(2) +>>> li +[1, 2] +>>> li.append(4) +>>> li +[1, 2, 4] +>>> li.append(3) +>>> li +[1, 2, 4, 3] +``` + +### List 切片 + + +列表切片的语法： + +```python +a_list[start:end] +a_list[start:end:step] +``` + +#### 切片 + +```python +>>> a = ['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'] +>>> a[2:5] +['bacon', 'tomato', 'ham'] +>>> a[-5:-2] +['egg', 'bacon', 'tomato'] +>>> a[1:4] +['egg', 'bacon', 'tomato'] +``` + +#### 省略索引 + +```python +>>> a[:4] +['spam', 'egg', 'bacon', 'tomato'] +>>> a[0:4] +['spam', 'egg', 'bacon', 'tomato'] +>>> a[2:] +['bacon', 'tomato', 'ham', 'lobster'] +>>> a[2:len(a)] +['bacon', 'tomato', 'ham', 'lobster'] +>>> a +['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'] +>>> a[:] +['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'] +``` + +#### 迈着大步 + +```python +['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'] +>>> a[0:6:2] +['spam', 'bacon', 'ham'] +>>> a[1:6:2] +['egg', 'tomato', 'lobster'] +>>> a[6:0:-2] +['lobster', 'tomato', 'egg'] +>>> a +['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'] +>>> a[::-1] +['lobster', 'ham', 'tomato', 'bacon', 'egg', 'spam'] +``` + +### 删除 + +```python +>>> li = ['bread', 'butter', 'milk'] +>>> li.pop() +'milk' +>>> li +['bread', 'butter'] +>>> del li[0] +>>> li +['butter'] +``` + +### 使用权 + +```python +>>> li = ['a', 'b', 'c', 'd'] +>>> li[0] +'a' +>>> li[-1] +'d' +>>> li[4] +Traceback (most recent call last): + File "", line 1, in +IndexError: list index out of range +``` + +### 连接 + + +```python +>>> odd = [1, 3, 5] +>>> odd.extend([9, 11, 13]) +>>> odd +[1, 3, 5, 9, 11, 13] +>>> odd = [1, 3, 5] +>>> odd + [9, 11, 13] +[1, 3, 5, 9, 11, 13] +``` + +### 排序和反转 + + +```python +>>> li = [3, 1, 3, 2, 5] +>>> li.sort() +>>> li +[1, 2, 3, 3, 5] +>>> li.reverse() +>>> li +[5, 3, 3, 2, 1] +``` + +### 计数 + +```python +>>> li = [3, 1, 3, 2, 5] +>>> li.count(3) +2 +``` + +### 重复 + +```python +>>> li = ["re"] * 3 +>>> li +['re', 're', 're'] +``` + +Python 流程控制 +------------ + +### 基本 + +```python +num = 5 +if num > 10: + print("num is totally bigger than 10.") +elif num < 10: + print("num is smaller than 10.") +else: + print("num is indeed 10.") +``` + +### 一行 + +```python +>>> a = 330 +>>> b = 200 +>>> r = "a" if a > b else "b" +>>> print(r) +a +``` + +### else if + +```python +value = True +if not value: + print("Value is False") +elif value is None: + print("Value is None") +else: + print("Value is True") +``` + +Python 循环 +-------- + +### 基础 + +```python +primes = [2, 3, 5, 7] +for prime in primes: + print(prime) +``` + +### 有索引 + +```python +animals = ["dog", "cat", "mouse"] +for i, value in enumerate(animals): + print(i, value) +``` + +### While + +```python +x = 0 +while x < 4: + print(x) + x += 1 # Shorthand for x = x + 1 +``` + +### Break + +```python +x = 0 +for index in range(10): + x = index * 10 + if index == 5: + break + print(x) +``` + +### Continue + +```python +for index in range(3, 8): + x = index * 10 + if index == 5: + continue + print(x) +``` + +### 范围 + +```python +for i in range(4): + print(i) # Prints: 0 1 2 3 +for i in range(4, 8): + print(i) # Prints: 4 5 6 7 +for i in range(4, 10, 2): + print(i) # Prints: 4 6 8 +``` + +### 使用 zip() + +```python +name = ['Pete', 'John', 'Elizabeth'] +age = [6, 23, 44] +for n, a in zip(name, age): + print('%s is %d years old' %(n, a)) +``` + +### 列表理解 + + +```python +result = [x**2 for x in range(10) if x % 2 == 0] + +print(result) +# [0, 4, 16, 36, 64] +``` + +Python 函数 +-------- + +### 基础 + +```python +def hello_world(): + print('Hello, World!') +``` + +### 返回 + +```python {3} +def add(x, y): + print("x is %s, y is %s" %(x, y)) + return x + y +add(5, 6) # => 11 +``` + +### 位置参数 + +```python +def varargs(*args): + return args +varargs(1, 2, 3) # => (1, 2, 3) +``` + +### 关键字参数 + +```python +def keyword_args(**kwargs): + return kwargs +# => {"big": "foot", "loch": "ness"} +keyword_args(big="foot", loch="ness") +``` + +### 返回多个 + +```python +def swap(x, y): + return y, x +x = 1 +y = 2 +x, y = swap(x, y) # => x = 2, y = 1 +``` + +### 默认值 + +```python +def add(x, y=10): + return x + y +add(5) # => 15 +add(5, 20) # => 25 +``` + +### 匿名函数 + +```python +# => True +(lambda x: x > 2)(3) +# => 5 +(lambda x, y: x ** 2 + y ** 2)(2, 1) +``` + +Python 模块 +-------- + +### 导入模块 + +```python +import math +print(math.sqrt(16)) # => 4.0 +``` + +### 从一个模块导入 + +```python +from math import ceil, floor +print(ceil(3.7)) # => 4.0 +print(floor(3.7)) # => 3.0 +``` + +### 全部导入 + +```python +from math import * +``` + +### 缩短模块 + +```python +import math as m +# => True +math.sqrt(16) == m.sqrt(16) +``` + +### 功能和属性 + +```python +import math +dir(math) +``` + +Python 文件处理 +---------- + +### 读取文件 + +#### 逐行 + +```python +with open("myfile.txt") as file: + for line in file: + print(line) +``` +#### 带行号 + +```python +file = open('myfile.txt', 'r') +for i, line in enumerate(file, start=1): + print("Number %s: %s" % (i, line)) +``` + + +### 字符串 + +#### 写一个字符串 + +```python +contents = {"aa": 12, "bb": 21} +with open("myfile1.txt", "w+") as file: + file.write(str(contents)) +``` + +#### 读取一个字符串 + +```python +with open('myfile1.txt', "r+") as file: + contents = file.read() +print(contents) +``` + +### 对象 + +#### 写一个对象 + +```python +contents = {"aa": 12, "bb": 21} +with open("myfile2.txt", "w+") as file: + file.write(json.dumps(contents)) +``` + +#### 读取对象 + +```python +with open('myfile2.txt', "r+") as file: + contents = json.load(file) +print(contents) +``` + +### 删除文件 + +```python +import os +os.remove("myfile.txt") +``` + +### 检查和删除 + +```python +import os +if os.path.exists("myfile.txt"): + os.remove("myfile.txt") +else: + print("The file does not exist") +``` + +### 删除文件夹 + +```python +import os +os.rmdir("myfolder") +``` + +Python 类和继承 +-------- + +### Defining + +```python +class MyNewClass: + pass +# Class Instantiation +my = MyNewClass() +``` + +### 构造函数 + +```python +class Animal: + def __init__(self, voice): + self.voice = voice + +cat = Animal('Meow') +print(cat.voice) # => Meow + +dog = Animal('Woof') +print(dog.voice) # => Woof +``` + +### 方法 + +```python +class Dog: + # 类的方法 + def bark(self): + print("Ham-Ham") + +charlie = Dog() +charlie.bark() # => "Ham-Ham" +``` + +### 类变量 + + +```python +class MyClass: + class_variable = "A class variable!" +# => 一个类变量！ +print(MyClass.class_variable) +x = MyClass() + +# => 一个类变量！ +print(x.class_variable) +``` + +### Super() 函数 + + +```python +class ParentClass: + def print_test(self): + print("Parent Method") + +class ChildClass(ParentClass): + def print_test(self): + print("Child Method") + # 调用父级的 print_test() + super().print_test() +``` +--- + +```python +>>> child_instance = ChildClass() +>>> child_instance.print_test() +Child Method +Parent Method +``` + +### repr() 方法 + +```python +class Employee: + def __init__(self, name): + self.name = name + + def __repr__(self): + return self.name + +john = Employee('John') +print(john) # => John +``` + +### 用户定义的异常 + +```python +class CustomError(Exception): + pass +``` + +### 多态性 + +```python +class ParentClass: + def print_self(self): + print('A') + +class ChildClass(ParentClass): + def print_self(self): + print('B') + +obj_A = ParentClass() +obj_B = ChildClass() + +obj_A.print_self() # => A +obj_B.print_self() # => B +``` + +### 覆盖 + +```python +class ParentClass: + def print_self(self): + print("Parent") + +class ChildClass(ParentClass): + def print_self(self): + print("Child") + +child_instance = ChildClass() +child_instance.print_self() # => Child +``` + +### 继承 + +```python +class Animal: + def __init__(self, name, legs): + self.name = name + self.legs = legs + +class Dog(Animal): + def sound(self): + print("Woof!") + +Yoki = Dog("Yoki", 4) +print(Yoki.name) # => YOKI +print(Yoki.legs) # => 4 +Yoki.sound() # => Woof! +``` + +各种各样的 +---------- + +### 注释 + +```python +# 这是单行注释 +``` +---------- + +```python +""" 可以写多行字符串 + 使用三个"，并且经常使用 + 作为文档。 +""" +``` +---------- +```python +''' 可以写多行字符串 + 使用三个'，并且经常使用 + 作为文档。 +''' +``` + +### 生成器 + +```python +def double_numbers(iterable): + for i in iterable: + yield i + i +``` + +生成器可帮助您编写惰性代码 + +### 要列出的生成器 + +```python +values = (-x for x in [1,2,3,4,5]) +gen_to_list = list(values) +# => [-1, -2, -3, -4, -5] +print(gen_to_list) +``` + +### 处理异常 + + +```python +try: + # 使用“raise”来引发错误 + raise IndexError("这是一个索引错误") +except IndexError as e: + pass # 通行证只是一个空操作。 通常你会在这里做恢复。 +except (TypeError, NameError): + pass # 如果需要，可以一起处理多个异常。 +else: # try/except 块的可选子句。 必须遵循除块之外的所有内容 + print("All good!") # 仅当 try 中的代码未引发异常时运行 +finally: # 在所有情况下执行 + print("我们可以在这里清理资源") +``` \ No newline at end of file