Python advanced

decorator

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def mydecorator(function):

    def wrapper(*args, **kwargs):
        function(*args, **kwargs)
        print(" I am decorating your funciton!")
        

    return wrapper

@mydecorator
def hello_world(name):
    print(f"Hello {name}")

hello_world("mike")

Example 1 保存调试信息

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def logged(function):
    def wrapper(*args, **kwargs):
        value = function(*args, **kwargs)
        with open("logfile.txt", "a+") as f:
            fname = function.__name__
            print(f"{fname} returned value {value}")
            f.write(f"{fname} returned value {value}\n")
        return value
    
    return wrapper
    
@logged
def add(x, y):
    return x + y

print(add(10, 20))

Example 2 计时

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import time

def timed(function):
    def wrapper(*args, **kwargs):
        before = time.time()
        value = function(*args, **kwargs)
        after = time.time()
        fname = function.__name__
        print(f"{fname} took {after - before} seconds to execute!")
        return value
    
    return wrapper

@timed
def myfunction(x):
    result = 1
    for i in range(1, x):
        result *= i
    return result

myfunction(1000)

generator

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def infinite_sequence():
    result = 1
    while True:
        yield result
        result *= 5

values = infinite_sequence()

for i in range(5):
    print(next(values))

argument parsing

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import sys
# Usage: python test.py filename

filename = sys.argv[1]
message = sys.argv[2]

with open(filename, "w+") as f:
    f.write(message)

或者

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import sys
import getopt

filename = "text.txt"
message = "Hello"

opts, args = getopt.getopt(sys.argv[1:],"f:m:", ["filename", "message"])

for opt, arg in opts:
    if opt == '-f':
        filename = arg
    if opt == '-m':
        message = arg

with open(filename, "w+") as f:
    f.write(message)

encapsulation

没有直接范围隐藏数据成员

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class Person:

    def __init__(self, name, age, gender):

        self.__name = name
        self.__age = age
        self.__gender = gender

    @property
    def Name(self):
        return self.__name
    
    @Name.setter # python 没有重载，只有这种
    def Name(self, value):
        if value == 'Bob':# 统一处理访问
            self.__name = 'Defult name'
        else:
            self.__name = value

    @staticmethod
    def mymethod():
        print("Hello World from static method!")

Person.mymethod()

p1 = Person('mike', 27, 'male')
print(p1.Name)

p1.Name = 'john'
print(p1.Name)

Type hinting

使用mypy做类型检查

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mypy .\test.py

使用显式类型标注

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def myfunction(myparameter:int) -> int:
    return myparameter + 10

print(myfunction(8))

def dosth(param: list[int]) -> list[int]:
    for i in range(len(param)):
        param[i] += 1

    return param

l = [1,2,3,4,5]

print(dosth(l))

Magic methods

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class Vector:

    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __add__(self, other):
        return(Vector(self.x + other.x, self.y + other.y))
    
    def __repr__(self) -> str:
        return f"X: {self.x}, Y: {self.y}"
    
    def __call__(self):
        print("Hello! I was called!")

v1 = Vector(10,20)
v2 = Vector(50,40)
v3 = v1 + v2
print(v3)
v3()