Python_裝飾器和生成器

sugarmo 發(fā)布于2019-07-30 15:40 / 2800人閱讀

摘要：迭代器迭代是訪問集合元素的一種方式。迭代器是一個可以記住遍歷的位置的對象，迭代器對象從集合的第一個元素開始訪問，直到所有的元素被訪問完結(jié)束，迭代器只往前不會往后退。生成器特點(diǎn)保存了一套生成數(shù)值的算法。

迭代器

迭代是訪問集合元素的一種方式。
迭代器是一個可以記住遍歷的位置的對象，迭代器對象從集合的第一個元素開始訪問，直到所有的元素被訪問完結(jié)束，迭代器只往前不會往后退。

可迭代對象

以直接作用域for循環(huán)的數(shù)據(jù)類型：

集合數(shù)據(jù)類型：list, tuple, dict, set, str

generator，包括生成器和yield的generator function

判斷是否可以迭代

使用方法isinstance()判斷一個對象是否具有Iterable對象

from collections import Iterable

isinstance("abc", Iterable) # true

迭代器

可以被next()函數(shù)調(diào)用并不斷返回下一個值的對象稱之為迭代器: Iterator

生成器, tuple

from collections import Iterator

isinstance((x for x in range(10)), Iterator) # True
isinstance([], Iterator) # False 列表不是迭代對象

iter()函數(shù)
生成器都是Iterator對象，但是list, dict, str雖然是Iterable,卻不是Iterator

可以把其他類型轉(zhuǎn)成生成器, 使用iter()函數(shù)

閉包

函數(shù)是引用

閉包:

def test(number):
    def test_in(number_in):
        print(number_in)
        return number + number_in
    return test_in

test(10)(20)

裝飾器

對函數(shù)或方法起裝飾作用

寫代碼要遵循開放封閉原則。
它規(guī)定已經(jīng)實(shí)現(xiàn)的功能代碼不允許被修改，但可以被擴(kuò)展。

封閉: 已實(shí)現(xiàn)的功能代碼塊
開放: 對擴(kuò)展開發(fā)

裝飾器原理：

def a(func):
    def inner():
        func()
    return inner()
    
def f1():
    print("f1")

f1 = a(f1) # 函數(shù)名作為變量名，重新賦值使用
f1()

裝飾器語法糖：

def a(func):
    def inner():
        func()
    return inner()

@a
def f1():
    print("f1")

f1()

二個裝飾器

def makeBold(fn):
    def warpped():
        print("1")
        return "" + fn() + ""
    return warpped

def makeItalic(fn):
    def warpped():
        print("2")
        return "" + fn() + ""
    return warpped

@makeBold
@makeItalic
def test1():
    print("3")
    return "hello world"

ret = test1()
print(ret)

# 輸出結(jié)果:
# 1
# 2
# 3
# hello world

裝飾器執(zhí)行的時間

def w1(func):
    print("1")
    def inner():
        print("2")
        func()
    return inner

def w2(func):
    print("4")
    def inner():
        print("5")
        func()
    return inner

@w2
@w1
def f1():
    print(3)

# 執(zhí)行f1
f1()
# 1 2 3 # 只有w1 裝飾
# 1 4 5 2 3 # w1,w2共同裝飾

# 不執(zhí)行f1
# 1 4

裝飾器對有參數(shù)、無參數(shù)函數(shù)進(jìn)行裝飾

def func(funName):
    print("1")
    def func_in(argA, argB): # 形參
        print("2")
        funName(argA, argB) # 調(diào)用傳遞參數(shù)
    return func_in


@func
def test(a, b):    
    print("a=%d,b=%d"%(a,b))

test(10, 20)

以*args來解決多參數(shù)問題

def func(funName):
    print("1")
    def func_in(*args, **kwargs): # 形參
        print("2")
        funName(*args, **kwargs) # 調(diào)用傳遞參數(shù)
    return func_in


@func
def test(a, b):    
    print("a=%d,b=%d"%(a,b))

test(10, 20)

裝飾器對帶有返回值的函數(shù)進(jìn)行裝飾

def func(funName):
    print("1")
    def func_in():
        print("2")
        return funName() # 返回值
    return func_in


@func
def test():    
    return "test"

ret = test()
print(ret)

通用裝飾器

def func(funName):
    def func_in(*args, **kwargs):
        return funName(*args, **kwargs) # 返回值
    return func_in


@func
def test():    
    return "test"

ret = test()
print(ret)

帶有參數(shù)裝飾器

from time import ctime, sleep

def timefun_arg(pre="hello"):
    def timefun(func):
        def warppedfunc():
            print("%s called at %s %s"%(func.__name__, ctime(), pre))
            return func()
        return warppedfunc
    return timefun


@timefun_arg("it") # 執(zhí)行，主動調(diào)用。需要多一層閉包函數(shù)
def foo():
    print("foo")

@timefun_arg("python")
def too():
    print("too")

foo()
sleep(2)
too()

作用域

globals

查看命名空間中所有全局變量：
globals()以字典方式返回

{"__name__": "__main__", "__doc__": None, "__package__": None, "__loader__": , "__spec__": None, "__annotations__": {}, "__builtins__": }

locals

查看命名空間中局部變量
locals()以字典方式返回：

{"__name__": "__main__", "__doc__": None, "__package__": None, "__loader__": , "__spec__": None, "__annotations__": {}, "__builtins__": }

LEGB規(guī)則

Python使用LEGB的順序來查找一個符號對應(yīng)的對象

locals -> enclosing function -> globals -> builtins

locals: 當(dāng)前所在的命名空間(如函數(shù)，模塊)，函數(shù)的參數(shù)也屬于命名空間內(nèi)的變量
enclosing: 外部嵌套函數(shù)的命名空間
globals: 全局變量，函數(shù)定義所在模塊的命名空間
builtins: 內(nèi)建模塊的命名空間

查看內(nèi)建模塊的變量：dir(__builtins__)

["ArithmeticError", "AssertionError", "AttributeError", "BaseException", "BlockingIOError", "BrokenPipeError", "BufferError", "BytesWarning", "ChildProcessError", "ConnectionAbortedError", "ConnectionError", "ConnectionRefusedError", "ConnectionResetError", "DeprecationWarning", "EOFError", "Ellipsis", "EnvironmentError", "Exception", "False", "FileExistsError", "FileNotFoundError", "FloatingPointError", "FutureWarning", "GeneratorExit", "IOError", "ImportError", "ImportWarning", "IndentationError", "IndexError", "InterruptedError", "IsADirectoryError", "KeyError", "KeyboardInterrupt", "LookupError", "MemoryError", "ModuleNotFoundError", "NameError", "None", "NotADirectoryError", "NotImplemented", "NotImplementedError", "OSError", "OverflowError", "PendingDeprecationWarning", "PermissionError", "ProcessLookupError", "RecursionError", "ReferenceError", "ResourceWarning", "RuntimeError", "RuntimeWarning", "StopAsyncIteration", "StopIteration", "SyntaxError", "SyntaxWarning", "SystemError", "SystemExit", "TabError", "TimeoutError", "True", "TypeError", "UnboundLocalError", "UnicodeDecodeError", "UnicodeEncodeError", "UnicodeError", "UnicodeTranslateError", "UnicodeWarning", "UserWarning", "ValueError", "Warning", "WindowsError", "ZeroDivisionError", "_", "__build_class__", "__debug__", "__doc__", "__import__", "__loader__", "__name__", "__package__", "__spec__", "abs", "all", "any", "ascii", "bin", "bool", "bytearray", "bytes", "callable", "chr", "classmethod", "compile", "complex", "copyright", "credits", "delattr", "dict", "dir", "divmod", "enumerate", "eval", "exec", "exit", "filter", "float", "format", "frozenset", "getattr", "globals", "hasattr", "hash", "help", "hex", "id", "input", "int", "isinstance", "issubclass", "iter", "len", "license", "list", "locals", "map", "max", "memoryview", "min", "next", "object", "oct", "open", "ord", "pow", "print", "property", "quit", "range", "repr", "reversed", "round", "set", "setattr", "slice", "sorted", "staticmethod", "str", "sum", "super", "tuple", "type", "vars", "zip"]

動態(tài)綁定

動態(tài)綁定屬性：

class Person(object):
    def __init__(self):
        pass
        
p1 = Person
p1.name = "pp" # 動態(tài)添加屬性

print(p1.name)

動態(tài)綁定方法：

import types
class Person(object):
        def __init__(self, newName, newAge):
                self.name = newName
                self.age = newAge
        def eat(self):
                print("eat-", self.name)

def run(self):
        print("run-", self.name)

p1 = Person("p1", 24)
p1.eat()

# 通過types庫中的MethodType方法來修改指向函數(shù)中的this指針
p1.run = types.MethodType(run, p1) # 動態(tài)添加方法

p1.run()

綁定靜態(tài)方法和靜態(tài)屬性：

class Person(object):
    def __init__(self):
        pass



@staticmethod
def test():
    print("static method")

Person.test = test # 綁定靜態(tài)方法
Person.name = "alogy" # 綁定靜態(tài)屬性

Person.test()

綁定類屬性：

class Person(object):
    def __init__(self):
        pass


@classmethod
def printNum(cls):
    print("class method")

Person.printNum = printNum

Person.printNum()

slots

動態(tài)語言：可以在運(yùn)行過程中，修改代碼
靜態(tài)語言：編譯時已經(jīng)確定好代碼，運(yùn)行過程中不能修改

__slots__作用：限制實(shí)例的屬性

class Person(object):
    __slots__ = ("name", "age")
    
p = Person()
p.name = "alogy"
p.age = 24

Note:
__slots__定義的屬性僅對當(dāng)前類實(shí)例起作用，對繼承的子類是不起作用

生成器

目標(biāo)：列表中有大量數(shù)據(jù)，還不想占用大量內(nèi)存空間。

生成器特點(diǎn)：保存了一套生成數(shù)值的算法。(什么時候需要使用到了，才去生成。)

生成器定義方法

方法1:()

a = (x for x in range(10))
print(a)

方法2: yield

def createNum():
    print("--start")
    a,b = 0,1
    for i in range(5):
        print("--11")
        yield b
        print("--22")
        a,b = b,a+b
        print("--33")
    print("--end")

t = createNum()

for num in t:
    print(num)

輸出結(jié)果：

--start
--11
1
--22
--33
--11
1
--22
--33
--11
2
--22
--33
--11
3
--22
--33
--11
5
--22
--33
--end

send方法: 與yield的結(jié)果配合使用，使得yield執(zhí)行的時候，外部可以傳遞參數(shù)到生成器中。
能夠執(zhí)行next()且還可以傳遞參數(shù)

def test():
    i = 0
    while i < 5:
        temp = yield i
        print(temp)
        i += 1

t = test()
print(t.next()) 
# 0
print(t.next()) 
# None
# 1
print(t.send("args"))
# args
# 2

Note:
send()第一次直接調(diào)用報錯，是參數(shù)不知道給那個函數(shù)。
報錯為：

Traceback (most recent call last):
  File "", line 1, in 
TypeError: can"t send non-None value to a just-started generator

解決方法：

通過next()先調(diào)用一次，然后再使用send()

第一次調(diào)用send(None)傳遞空值進(jìn)去，后續(xù)幾次傳遞該傳遞的值

完成多任務(wù)

def test1():
    while True:
        print("test1")
        yield None

def test2():
    while True:
        print("test2")
        yield None

t1 = test1()
t2 = test2()

while True:
    t1.next()
    t2.next()

一齊執(zhí)行test1(),test2(),test3(),三個while True同時執(zhí)行
三個多任務(wù)或者三個以上同時執(zhí)行稱之為：協(xié)程