`python`定制類主要是實現(xiàn)特定功能，通過在類中定義特定的函數(shù)完成特定的功能。

class Student(object):def __init__(self, name):self.name =namestudent = Student("lilei") print(student)

`實現(xiàn)定制類`

class Student(object):def __init__(self, name):self.name = namedef __str__(self):return ("self name is %s" %(self.name))student2 = Student("hanmeimei") print(student2)

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實現(xiàn)`__str__`函數(shù)，可以在print類對象時打印指定信息

通過實現(xiàn)`__iter__`和`__next__`同樣可以使類對象產(chǎn)生可迭代序列，下面實現(xiàn)了`斐波那契數(shù)列`

class Fib(object):def __init__(self):self.a , self.b = 0,1def __iter__(self):return selfdef __next__(self):self.a, self.b = self.b, self.a+ self.bf self.a > 30:raise StopIteration()return self.a

打印輸出

for n in Fib():print(n)

可以實現(xiàn)`__getitem__`函數(shù),這樣就可以按照索引訪問類對象中迭代元素了。

class OddNum(object):def __init__(self):self.num = -1def __iter__(self):return selfdef __next__(self):self.num = self.num +2if self.num > 10:raise StopIteration()return self.num def __getitem__(self,n):temp = 1for i in range(n):temp += 2return temp

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for n in OddNum():print(n)oddnum = OddNum() print(oddnum[3])

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可以進一步完善OddNum類的`__getitem__`函數(shù)，使其支持`切片處理`

def __getitem__(self, n):if isinstance(n ,int):temp =1for i in range(n):temp +=2return tempif isinstance(n, slice):start = n.startend = n.stopif start is None:start = 0tempList = []temp = 1for i in range(end):if i >= start:temp += 2tempList.append(temp)return tempList

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`print(oddnum[1:4])`
通過實現(xiàn)`__getattr__`函數(shù)，可以在類對象中沒有某個屬性時，自動調(diào)用`__getattr__`函數(shù)
實現(xiàn)`__call__`函數(shù)，可以實現(xiàn)類對象的函數(shù)式調(diào)用

def __getattr__(self,attr):if attr == 'name':return 'OddNum'if attr == 'data':return lambda:self.numraise AttributeError('\'OddNum\' object has no attribute \'%s\'' %attr) def __call__(self):return "My name is OddNum!!"

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只有在沒有找到屬性的情況下，才調(diào)用`__getattr__`，已有的屬性不會在`__getattr__`中查找。

print(oddnum.name) print(oddnum.data) #沒有func函數(shù)會拋出異常 #print(oddnum.func) #可以直接通過oddnum()函數(shù)式調(diào)用 print(oddnum())

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下面是廖雪峰官方網(wǎng)站上的一個鏈式轉(zhuǎn)化例子，用到了這些特定函數(shù)

class Chain(object):def __init__(self, path=''):self.path = pathdef __getattr__(self,attr):return Chain('%s/%s'%(self.path, attr))def users(self, users):return Chain('%s/users/%s' %(self.path, users))def __str__(self):return self.path__repr__ = __str__print(Chain().users('michael').repos)

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class Chain(object):def __init__(self, path=''):self.path = pathdef __getattr__(self,attr):return Chain('%s/%s'%(self.path, attr))def __call__(self, param):return Chain('%s/%s'%(self.path, param))def __str__(self):return self.path__repr__ = __str__print(Chain().get.users('michael').group('doctor').repos)

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python同樣支持`枚舉`操作

from enum import EnumMonth = Enum('Month', ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'))for name, member in Month.__members__.items():print(name, '=>', member, ',', member.value)from enum import Enum Month = Enum('Month', ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec') ) for name, member in Month.__members__.items():print(name, '=>', member, ',', member.value)from enum import unique @unique class Weekday(Enum):Sun = 0 # Sun的value被設定為0Mon = 1Tue = 2Wed = 3Thu = 4Fri = 5Sat = 6for name , member in Weekday.__members__.items():print(name, '=>', member, ',', member.value)

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轉(zhuǎn)載于:https://www.cnblogs.com/secondtonone1/p/7458805.html

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