Python 3 最常用函数（最全的查询）

叁歲伎倆 2024-03-31 16:22 44阅读 0赞

**介绍**

*  Python (python.org)
 *  Learn X in Y minutes (learnxinyminutes.com)
 *  Regex in python (quickref.me)

**Hello World**

>>> print("Hello, World!")

Hello, World!

Python 中著名的“Hello World”程序

**变量**

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**

<table> 
 <tbody> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> str </td> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> Text </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> int, float, complex </td> 
 <td style="vertical-align:top;"> Numeric </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> list, tuple, range </td> 
 <td style="vertical-align:top;"> Sequence </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> dict </td> 
 <td style="vertical-align:top;"> Mapping </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> set, frozenset </td> 
 <td style="vertical-align:top;"> Set </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> bool </td> 
 <td style="vertical-align:top;"> Boolean </td> 
 </tr> 
 <tr> 
 <td style="border-color:#e8e8e8;vertical-align:top;"> bytes, bytearray, memoryview </td> 
 <td style="vertical-align:top;"> Binary </td> 
 </tr> 
 </tbody> 
</table>

查看: Data Types

**Slicing String**

>>> msg = "Hello, World!"

>>> print(msg\[2:5\])

llo

查看: Strings

**Lists**

mylist = \[\]

mylist.append(1)

mylist.append(2)

for item in mylist:

print(item) \# 打印输出 1,2

查看: Lists

**If Else**

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

**循环**

for item in range(6):

if item == 3: break

print(item)

else:

print("Finally finished!")

查看: Loops

**函数**

>>> def my\_function():

...  print("来自函数的你好")

...

>>> my\_function()

来自函数的你好

查看: Functions

**文件处理**

with open("myfile.txt", "r", encoding='utf8') as file:

for line in file:

print(line)

查看: 文件处理

**算术**

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

**加等于**

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+)**

>>> 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** **数据类型**

**字符串**

hello = "Hello World"

hello = 'Hello World'

multi\_string = """Multiline Strings

Lorem ipsum dolor sit amet,

consectetur adipiscing elit """

查看: Strings

**数字**

x = 1 \# int

y = 2.8 \# float

z = 1j \# complex

>>> print(type(x))

**布尔值**

my\_bool = True

my\_bool = False

bool(0) \# => False

bool(1) \# => True

**Lists**

list1 = \["apple", "banana", "cherry"\]

list2 = \[True, False, False\]

list3 = \[1, 5, 7, 9, 3\]

list4 = list((1, 5, 7, 9, 3))

查看: Lists

**元组 Tuple**

my\_tuple = (1, 2, 3)

my\_tuple = tuple((1, 2, 3))

类似于 List 但不可变

**Set**

set1 = \{ "a", "b", "c"\}

set2 = set(("a", "b", "c"))

一组独特的项目/对象

**字典 Dictionary**

>>> empty\_dict = \{\}

>>> a = \{ "one": 1, "two": 2, "three": 3\}

>>> a\["one"\]

>>> 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\['four'\]

Key：值对，JSON 类对象

**Casting**

**整数 Integers**

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**

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**

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**

>>> hello = "Hello, World"

>>> print(hello\[1\])

>>> print(hello\[-1\])

获取位置 1 或最后的字符

**循环**

>>> for char in "foo":

... print(char)

遍历单词 foo 中的字母

**切片字符串**

┌───┬───┬───┬───┬───┬───┬───┐

| m | y | b | a | c | o | n |

└───┴───┴───┴───┴───┴───┴───┘

0 1 2 3 4 5 6 7

\-7 \-6 \-5 \-4 \-3 \-2 \-1

--------------------

>>> s = 'mybacon'

>>> s\[2:5\]

'bac'

>>> s\[0:2\]

'my'

--------------------

>>> s = 'mybacon'

>>> s\[:2\]

'my'

>>> s\[2:\]

'bacon'

>>> s\[:2\] + s\[2:\]

'mybacon'

>>> s\[:\]

'mybacon'

--------------------

>>> s = 'mybacon'

>>> s\[-5:-1\]

'baco'

>>> s\[2:6\]

'baco'

**迈着大步**

>>> s = '12345' \* 5

>>> s

'1234512345123451234512345'

>>> s\[::5\]

'11111'

>>> s\[4::5\]

'55555'

>>> s\[::-5\]

'55555'

>>> s\[::-1\]

'5432154321543215432154321'

**字符串长度**

>>> hello = "Hello, World!"

>>> print(len(hello))

len() 函数返回字符串的长度

**多份**

>>> s = '===+'

>>> n = 8

>>> s \* n

'===+===+===+===+===+===+===+===+'

**检查字符串**

>>> s = 'spam'

>>> s in 'I saw spamalot!'

True

>>> s not in 'I saw The Holy Grail!'

True

**连接**

>>> s = 'spam'

>>> t = 'egg'

>>> s + t

'spamegg'

>>> 'spam' 'egg'

'spamegg'

**格式化**

name = "John"

print("Hello, %s!" % name)

--------------------

name = "John"

age = 23

print("%s is %d years old." % (name, age))

**format()** **方法**

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**

>>> name = input("Enter your name: ")

Enter your name: Tom

>>> name

'Tom'

从控制台获取输入数据

**Join** **加入**

>>> "\#".join(\["John", "Peter", "Vicky"\])

'John\#Peter\#Vicky'

**Endswith** **以..结束**

>>> "Hello, world!".endswith("!")

True

**Python F** **字符串（自 Python 3.6+ 起）**

**f-Strings** **用法**

>>> 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

**f-Strings** **填充对齐**

>>> 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**

>>> 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**

>>> f'\{ 12345:+\}' \# \[sign\] (+/-)

'+12345'

>>> f'\{ \-12345:+\}'

'-12345'

>>> f'\{ \-12345:+10\}'

' -12345'

>>> f'\{ \-12345:+010\}'

'-000012345'

**F-Strings** **其它**

>>> 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**

>>> 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**

>>> 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**

>>> 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：

a\_list\[start:end\]

a\_list\[start:end:step\]

**切片**

>>> 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**

>>> 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**

\['spam', 'egg', 'bacon', 'tomato', 'ham', 'lobster'\]

>>> 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**

>>> li = \['bread', 'butter', 'milk'\]

>>> li.pop()

'milk'

>>> li

\['bread', 'butter'\]

>>> del li\[0\]

>>> li

\['butter'\]

**使用权**

>>> li = \['a', 'b', 'c', 'd'\]

>>> li\[0\]

'a'

>>> li\[-1\]

'd'

>>> li\[4\]

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

IndexError: list index out of range

**连接**

>>> 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**

>>> li = \[3, 1, 3, 2, 5\]

>>> li.sort()

>>> li

\[1, 2, 3, 3, 5\]

>>> li.reverse()

>>> li

\[5, 3, 3, 2, 1\]

**计数**

>>> li = \[3, 1, 3, 2, 5\]

>>> li.count(3)

**重复**

>>> li = \["re"\] \* 3

>>> li

\['re', 're', 're'\]

**Python** **流程控制**

**基本**

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**

>>> a = 330

>>> b = 200

>>> r = "a" if a > b else "b"

>>> print(r)

**else if**

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**

primes = \[2, 3, 5, 7\]

for prime in primes:

print(prime)

**有索引**

animals = \["dog", "cat", "mouse"\]

for i, value in enumerate(animals):

print(i, value)

**While**

x = 0

while x < 4:

print(x)

x \+= 1 \# Shorthand for x = x + 1

**Break**

x = 0

for index in range(10):

x = index \* 10

if index == 5:

break

print(x)

**Continue**

for index in range(3, 8):

x = index \* 10

if index == 5:

continue

print(x)

**范围**

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()**

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**

result = \[x\*\*2 for x in range(10) if x % 2 == 0\]

print(result)

\# \[0, 4, 16, 36, 64\]

**Python** **函数**

**基础**

def hello\_world():

print('Hello, World!')

**返回**

def add(x, y):

print("x is %s, y is %s" %(x, y))

return x + y

add(5, 6) \# => 11

**位置参数**

def varargs(\*args):

return args

varargs(1, 2, 3) \# => (1, 2, 3)

**关键字参数**

def keyword\_args(\*\*kwargs):

return kwargs

\# => \{ "big": "foot", "loch": "ness"\}

keyword\_args(big="foot", loch="ness")

**返回多个**

def swap(x, y):

return y, x

x = 1

y = 2

x, y = swap(x, y) \# => x = 2, y = 1

**默认值**

def add(x, y=10):

return x + y

add(5) \# => 15

add(5, 20) \# => 25

**匿名函数**

\# => True

(lambda x: x > 2)(3)

\# => 5

(lambda x, y: x \*\* 2 \+ y \*\* 2)(2, 1)

**Python** **模块**

**导入模块**

import math

print(math.sqrt(16)) \# => 4.0

**从一个模块导入**

from math import ceil, floor

print(ceil(3.7)) \# => 4.0

print(floor(3.7)) \# => 3.0

**全部导入**

from math import \*

**缩短模块**

import math as m

\# => True

math.sqrt(16) == m.sqrt(16)

**功能和属性**

import math

dir(math)

**Python** **文件处理**

**读取文件**

**逐行**

with open("myfile.txt") as file:

for line in file:

print(line)

**带行号**

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**

contents = \{ "aa": 12, "bb": 21\}

with open("myfile1.txt", "w+") as file:

file.write(str(contents))

**读取一个字符串**

with open('myfile1.txt', "r+") as file:

contents = file.read()

print(contents)

**对象**

**写一个对象**

contents = \{ "aa": 12, "bb": 21\}

with open("myfile2.txt", "w+") as file:

file.write(json.dumps(contents))

**读取对象**

with open('myfile2.txt', "r+") as file:

contents = json.load(file)

print(contents)

**删除文件**

import os

os.remove("myfile.txt")

**检查和删除**

import os

if os.path.exists("myfile.txt"):

os.remove("myfile.txt")

else:

print("The file does not exist")

**删除文件夹**

import os

os.rmdir("myfolder")

**Python** **类和继承**

**Defining**

class MyNewClass:

pass

\# Class Instantiation

my = MyNewClass()

**构造函数**

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**

class Dog:

\# 类的方法

def bark(self):

print("Ham-Ham")

charlie = Dog()

charlie.bark() \# => "Ham-Ham"

**类变量**

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**

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()

--------------------

>>> child\_instance = ChildClass()

>>> child\_instance.print\_test()

Child Method

Parent Method

**repr()** **方法**

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**

class CustomError(Exception):

pass

**多态性**

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**

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**

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**

\# 这是单行注释

--------------------

""" 可以写多行字符串

使用三个"，并且经常使用

作为文档。

"""

--------------------

''' 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**

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**

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**

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")

Python 3 最常用函数（最全的查询）

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