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python学习笔记(基本语法+脚本)

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​ 个人学习python的笔记！基于 python3 ! 相关文档可以参考: https://docs.python.org/zh-cn/3/library/index.html , 本地可以执行python3 -m pydoc -p 1234 打开文档

基本语法

1. 简单控制语句

字符串推荐用 '' 单引号引用

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list: List[int] = [1, 2, 3]
for elem in list:
    if elem > 1:
        print(f'data {elem} > 1')  # 这里是format语句，属于语法糖
    else:
        print(f'data {elem} < 1')

'''
data 1 < 1
data 2 > 1
data 3 > 1
'''

2. 异常

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x = -1
try:
    if x < 0:
        raise Exception("Sorry, no numbers below zero")
except Exception as err:
    print("find err: %s" % err)
'''
find err: Sorry, no numbers below zero
'''

3. 推导式(比较晦涩难懂)

推导式好处: 效率更高，底层是c执行

1. 列表推导式

一共两种形式：(参考: https://zhuanlan.zhihu.com/p/139621170) ， 它主要是输出是列表(list)

  • [x for x in data if condition] 这里的含义是data只有满足if条件中的情况才保留 (if)

  • [exp1 if condition else exp2 for x in data] ， 这里的含义是data满足if条件时执行exp1 否则 exp2 （if - else）

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import re

"""
获取所有的数字
"""
list = ["1", "2", "3", "4", "5", "a", "b", "c"]
print([elem for elem in list if re.match("\\d", elem)])
'''
['1', '2', '3', '4', '5']
'''

"""
获取所有的字母
"""
print([elem for elem in list if re.match("[a-z]", elem)])
'''
['a', 'b', 'c']
'''

"""
如果元素是数字则存储，否则则upper
"""
print([elem if re.match("\\d", elem) else elem.upper() for elem in list])
'''
['1', '2', '3', '4', '5', 'A', 'B', 'C']
'''

最佳实践： 参考(https://github.com/httpie/httpie/blob/master/httpie/core.py#L235)

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def decode_raw_args(
        args: List[Union[str, bytes]],
        stdin_encoding: str
) -> List[str]:
    """
    Convert all bytes args to str
    by decoding them using stdin encoding.

    """
    return [
        arg.decode(stdin_encoding)
        if type(arg) is bytes else arg
        for arg in args
    ]


def decode_raw_args_parse(
        args: List[Union[str, bytes]],
        stdin_encoding: str
) -> List[str]:
    """
    Convert all bytes args to str
    by decoding them using stdin encoding.
    不使用推导式
    """
    result: List[str] = []
    for arg in args:
        if type(arg) is bytes:
            result.append(arg.decode(stdin_encoding))
        else:
            result.append(arg)
    return result


# arg.decode(stdin_encoding) if type(arg) is bytes else arg for arg in args
print(decode_raw_args(args=[b'111', b'222'], stdin_encoding="utf-8"))
print(decode_raw_args(args=["111", "222"], stdin_encoding=""))
'''
['111', '222']
['111', '222']
'''

print(decode_raw_args_parse(args=[b'111', b'222'], stdin_encoding="utf-8"))
print(decode_raw_args_parse(args=["111", "222"], stdin_encoding=""))
'''
['111', '222']
['111', '222']
'''

2. 字典推导式

{ key_expr: value_expr for value in collection if condition } ，输出是 dict

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"""
{ key_expr: value_expr for value in collection if condition }

反转key value，且获取 value 为在set {'a', 'b', 'c'}中的元素
"""
dict_old = {'a': 'A', 'b': 'B', 'c': 'C', 'd': 'D'}
print({dict_old[value]: value for value in dict_old if value in {'a', 'b', 'c'}})
'''
{'A': 'a', 'B': 'b', 'C': 'c'}
'''

print({key: value for value, key in dict_old.items() if value in {'a', 'b', 'c'}})
'''
{'A': 'a', 'B': 'b', 'C': 'c'}
'''

3. 集合推导式

表达式:

  • { expr for value in collection if condition }
  • {exp1 if condition else exp2 for x in data}

输出是 set

其实就是上面列表推导式 [] 换成 {} ，输出由 list 变成了 set

4. for 循环 迭代器

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import os
from collections.abc import Iterable

with open("text.log", "wt") as file:
    file.truncate()
    file.writelines("line 1" + os.linesep)
    file.writelines("line 2" + os.linesep)
    file.writelines("line 3" + os.linesep)
    pass

with open("text.log", "rt") as file:
    for line in file:
        print("type: {type}, isinstance: {isinstance}, line: {line}".format(type=type(file),
                                                                            isinstance=isinstance(file, Iterable),
                                                                            line=line))
    pass

'''
type: <class '_io.TextIOWrapper'>, isinstance: True, line: line 1

type: <class '_io.TextIOWrapper'>, isinstance: True, line: line 2

type: <class '_io.TextIOWrapper'>, isinstance: True, line: line 3
'''

这里面 _io.TextIOWrapper 实现了 __next__() 方法

比如我们自己实现一个可迭代的对象

下面可以看到我使用了类型申明 List[str] 其实这个python运行时并不会检测，需要工具进行检测！

变量默认都是 Any 类型 ，具体可以看 https://docs.python.org/zh-cn/3/library/typing.html

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from typing import List

class Items(object):
    def __init__(self, list: List[str]):
        self.list = list
        self.index = 0

    def __next__(self, *args, **kwargs):
        """
        next，没有抛出StopIteration
        """
        if self.index >= len(self.list):
            raise StopIteration
        result = self.list[self.index]
        self.index = self.index + 1
        return result

    def __iter__(self, *args, **kwargs):
        """
        返回一个迭代器
        """
        return self


data = Items(["1", "2", "3"])

for x in data:
    print(x)
'''
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'''

5. 包管理

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from ..a import foo  # 上级目录
from .a import foo_a  # 当前目录

import sys  # 引用源码或者lib
from copy import deepcopy  # 引用源码或者lib

from pygments.formatters.terminal import TerminalFormatter  # 引用 lib.lib.file

import demo.utils.a


def c_foo():
    demo.utils.a.foo_a()
    TerminalFormatter()
    deepcopy()
    print(sys.api_version)


def b_foo():
    foo()

基本数据类型

1. 定义方式

  • mylist: list[str] = ["apple", "banana", "cherry"]
  • mylist=["apple", "banana", "cherry"]
Text Type:str
Numeric Types:int, float, complex
Sequence Types:list, tuple, range
Mapping Type:dict
Set Types:set, frozenset
Boolean Type:bool
Binary Types:bytes, bytearray, memoryview

2. 数字基本类型

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x = 1  # int
y = 1.1  # float
z = 1j  # 复数(complex)
a = complex(1, 2)  # 复数(complex)
print(type(x))
print(type(y))
print(type(z))
print(z.imag, z.real)
print(type(a))
print(a.imag, a.real)
'''
<class 'int'>
<class 'float'>
<class 'complex'>
1.0 0.0
<class 'complex'>
2.0 1.0
'''

3. 字符串

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str = "hello"
print(str)
print(str[0:])
print(str[:5])
print(str[:-1])
print(str[0:5])
print(str[0:5:1])
print(str[0:5:2])
'''
hello
hello
hello
hell
hello
hello
hlo
'''

# format
print("My name is {} and age is {}".format("tom", 18))
'''
My name is tom and age is 18
'''

quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))
'''
I want to pay 49.95 dollars for 3 pieces of item 567.
'''

# func
str = "hello world! "
print(str.upper())
print(str.lower())
print(str.strip())
print(str + " ...")
'''
HELLO WORLD! 
hello world! 
hello world!
hello world!  ...
'''

# format
myorder = "I have a {carname}, it is a {model}."
print(myorder.format(carname="Ford", model="Mustang"))
'''
I have a Ford, it is a Mustang.
'''

4. lambda

其实就是一个func

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def add(num):
    return lambda x: x + num


print(add(10)(10))
'''
20
'''

lanbda 例子2

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import json

class Obj:
    def __init__(self):
        self.name = "tom"
        self.age = 1


print(json.dumps(Obj(), default=lambda obj: obj.__dict__))
'''
{"name": "tom", "age": 1}
'''

集合

list, tuple, range, dict, set, frozenset

  • list , 例如: mylist = ["apple", "banana", "cherry"]
  • tuple 是特殊的数组，就是不能改变， 例如 mytuple = ("apple", "banana", "cherry")
  • range 可以理解是个迭代器, 例如：
  • dict 就是个map， 例如： thisdict = {"brand": "Ford", "model": "Mustang", "year": 1964}
  • set 就是个去重复的list , 例如： myset = {"apple", "banana", "cherry"}

1. list

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mylist = ["apple", "banana", "cherry"]

# 切片
print(mylist[0])
print(mylist[2])
print(mylist[-1])
print(mylist[0:3:2])
'''
apple
cherry
cherry
['apple', 'cherry']
'''

# 基本操作
mylist.append("orange")
print(mylist)
'''
['apple', 'banana', 'cherry', 'orange']
'''

mylist.insert(0, "mango")
print(mylist)
'''
['mango', 'apple', 'banana', 'cherry', 'orange']
'''

# 循环
for x in mylist:
    print(x)

'''
apple
banana
cherry
orange
'''

for index in range(len(mylist)):
    print("index: %d" % index)
'''
index: 0
index: 1
index: 2
index: 3
index: 4
'''

if "apple" in mylist:
    print("success!")

'''
success!
'''

# [执行表达式(也就是for循环中的，如果有if则是if中执行的), for item in list 条件表达式]
new_list = [elem.upper() for elem in mylist if "a" in elem]  # contains 'a' char elem str
print(new_list)
'''
['MANGO', 'APPLE', 'BANANA', 'ORANGE']
'''

newList = []
for elem in mylist:
    if 'a' in elem:
        newList.append(elem.upper())
print(newList)
'''
['MANGO', 'APPLE', 'BANANA', 'ORANGE']
'''

2. map

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thisdict = {"brand": "Ford", "model": "Mustang", "year": 1964}

for key, value in thisdict.items():
    print("key: {}, value: {}".format(key, value))

'''
key: brand, value: Ford
key: model, value: Mustang
key: year, value: 1964
'''

for key in thisdict:
    print("key: {}, value: {}".format(key, thisdict[key]))
'''
key: brand, value: Ford
key: model, value: Mustang
key: year, value: 1964
'''

3. range

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# range 会生成一个迭代器，(start,end,sep) ， 左闭右开
for x in range(6):  # [0,1,2,3,4,5]
    print("x is %d" % x)
'''
x is 0
x is 1
x is 2
x is 3
x is 4
x is 5
'''

for x in range(2, 6):
    print("x is %d" % x)

'''
x is 2
x is 3
x is 4
x is 5
'''

for x in range(1, 6, 2):
    print("x is %d" % x)
'''
x is 1
x is 3
x is 5
'''

方法

1. 定义一个空方法

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def func_1():
    pass  # 空方法必须申明pass


func_1()

2. 参数

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# name 为必须添的参数，不然为空会报错
# age 为默认参数
# agrs 为可变参数
# kwargs 为 k v 参数
def func_1(name, age=1, *args, **kwargs):
    print("name: %s" % name)
    print("age: %d" % age)
    print("len(args): {}, type: {}".format(len(args), type(args)))
    for value in args:
        print("args value: {}".format(value))

    print("len(kwargs): {}, type: {}".format(len(kwargs), type(kwargs)))
    for key, value in kwargs.items():
        print("kwargs key: {}, value: {}".format(key, value))


func_1(name="tom", age=10, args="1", kwargs="2")
'''
name: tom
age: 10
len(args): 0
len(kwargs): 0, type: <class 'tuple'>
len(kwargs): 2, type: <class 'dict'>
kwargs key: args, value: 1
kwargs key: kwargs, value: 2
'''

# 这里注意由于dict所以不能申明kv
func_1("tom", 10, "1", "2", args="1", kwargs="2")
'''
name: tom
age: 10
len(args): 2, type: <class 'tuple'>
args value: 1
args value: 2
len(kwargs): 2, type: <class 'dict'>
kwargs key: args, value: 1
kwargs key: kwargs, value: 2
'''

3. 类型

申明输入输出类型

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from typing import List, Union
def decode_raw_args(
    args: List[Union[str, bytes]],
    stdin_encoding: str
) -> List[str]:
    """
    Convert all bytes args to str
    by decoding them using stdin encoding.

    """
    return [
        arg.decode(stdin_encoding)
        if type(arg) is bytes else arg
        for arg in args
    ]

类

1. 定义类和方法

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# 如果没有父类继承，这里选择 object，比较规范
class Person(object):
    # gender none, male or female
    gender = "none"

    # 构造器
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def my_name(self):
        return self.name


p = Person(name="tome", age=1)
print(p.my_name())

2. 类型的继承

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import json


class Person(object):
    # gender none, male or female
    gender = "none"

    # 构造器
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def my_name(self):
        return self.name


p = Person(name="tome", age=1)
print(p.my_name())


class Mail(Person):
    def __init__(self, name, age):
        super(Mail, self).__init__(name, age)
        self.gender = "mail"

    def my_name(self):
        return self.name + "_mail"


p = Mail(name="tome", age=1)
print(json.dumps(p, default=lambda obj: obj.__dict__))
print(p.my_name())

3. 类 __new__ 函数

主要是__init__执行前会调用

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#!/usr/bin/python

import json


class Person(object):
    def __new__(cls, *args, **kwargs):
        instance = object.__new__(cls)
        instance.job = "it"
        return instance

    # construct
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def to_json(self):
        return json.dumps(self, default=lambda obj: obj.__dict__)


p = Person(name="tome", age=1)
print(p.to_json()) # {"age": 1, "job": "it", "name": "tome"}

其他用法技巧

1. 断言

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if type(1) is int:
    print("args is int")
    ...  # 等效 pass
'''
args is int
'''

2. 测试 <<<

可以参考文件: https://segmentfault.com/q/1010000010389542 , 属于doctest

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def humanize_bytes(n, precision=2):
    # Author: Doug Latornell
    # Licence: MIT
    # URL: https://code.activestate.com/recipes/577081/
    """Return a humanized string representation of a number of bytes.

    >>> humanize_bytes(1)
    '1 B'
    >>> humanize_bytes(1024, precision=1)
    '1.0 kB'
    >>> humanize_bytes(1024 * 123, precision=1)
    '123.0 kB'
    >>> humanize_bytes(1024 * 12342, precision=1)
    '12.1 MB'
    >>> humanize_bytes(1024 * 12342, precision=2)
    '12.05 MB'
    >>> humanize_bytes(1024 * 1234, precision=2)
    '1.21 MB'
    >>> humanize_bytes(1024 * 1234 * 1111, precision=2)
    '1.31 GB'
    >>> humanize_bytes(1024 * 1234 * 1111, precision=1)
    '1.3 GB'

    """
    abbrevs = [
        (1 << 50, 'PB'),
        (1 << 40, 'TB'),
        (1 << 30, 'GB'),
        (1 << 20, 'MB'),
        (1 << 10, 'kB'),
        (1, 'B')
    ]

    if n == 1:
        return '1 B'

    for factor, suffix in abbrevs:
        if n >= factor:
            break

    # noinspection PyUnboundLocalVariable
    return f'{n / factor:.{precision}f} {suffix}'

3. yield

其实类似于程序的断电，比如程序运行到那里其实是返回一个生成器，然后当你下一步是才会执行，比较节省内存

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from typing import List


def new(size: int = 1024 * 1024):
    yield new_data(size)


def new_data(size: int) -> List[int]:
    return [0] * size


data = new()
print(type(data))
print(len(next(data)))  # 只能执行一次 next不然报错
'''
<class 'generator'>
1048576
'''

脚本

base64输出

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echo "aGVsbG8gcHl0aG9uCg==" | python -c "import sys,base64; print(sys.stdin.read())"

->

echo "aGVsbG8gcHl0aG9uCg==" | python -c "import sys,base64; print(base64.b64decode(sys.stdin.read()))"
-> stdout:
b'hello python\n'

文件操作

  • r , w, x ,a四种类型(a: append, w=truncate+create, x=truncate+create if not exit)
  • b,t 文件类型

第一列可以和第二列文件类型组合，第一列不允许并存

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import os


with open("file.log", "w") as file:
    for x in range(0, 100):
        file.write("hello world"+os.linesep)


with open("file.log","r") as file:
    for line in file.readlines():
        print(line)

json

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import json

print(json.dumps({"k1": "v1", "k2": [1, 2, 3]}))
print(json.loads('{"k1": "v1", "k2": [1, 2, 3]}'))

如果是class，需要继承 JSONEncoder和JSONDecoder实现子类 ，或者

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import json, datetime

class Demo(object):
    def __init__(self, name: str, age: int, birthday: datetime.date):
        self.name = name
        self.agw = age
        self.birthday = birthday

    def to_json(self, _):
        return {"name": self.name, "age": self.agw, "birthday": self.birthday.strftime("%Y-%m-%d")}


data = Demo("tom", 18, datetime.date(2001, 1, 1))
print(json.dumps(data, default=data.to_json))

typing (申明类型)

官方文档： https://docs.python.org/zh-cn/3/library/typing.html

可以参考这篇文章： https://sikasjc.github.io/2018/07/14/type-hint-in-python/

对于喜欢静态类型的语言，我觉得是非常nice的

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from typing import Dict, List


def test(data: Dict[str, str]) -> List[str]:
    return [x for x in data]


print(test({"k1": "v1", "k2": "v2"}))
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