Python 类和对象相关的内置函数
【摘要】 类和对象相关的内置函数知识！
1、__str__和__repr__
改变对象的字符串显示__str__,__repr__
自定制格式化字符串__format__
#_*_coding:utf-8_*_
format_dict={
'nat':'{obj.name}-{obj.addr}-{obj.type}',#学校名-学校地址-学校类型
'tna':'{obj.type}:{obj.name}:{obj.addr}',#学校类型:学校名:学校地址
'tan':'{obj.type}/{obj.addr}/{obj.name}',#学校类型/学校地址/学校名
}
class School:
def __init__(self,name,addr,type):
self.name=name
self.addr=addr
self.type=type
def __repr__(self):
return 'School(%s,%s)' %(self.name,self.addr)
def __str__(self):
return '(%s,%s)' %(self.name,self.addr)
def __format__(self, format_spec):
# if format_spec
if not format_spec or format_spec not in format_dict:
format_spec='nat'
fmt=format_dict[format_spec]
return fmt.format(obj=self)
s1=School('oldboy1','北京','私立')
print('from repr: ',repr(s1))
print('from str: ',str(s1))
print(s1)
'''
str函数或者print函数--->obj.__str__()
repr或者交互式解释器--->obj.__repr__()
如果__str__没有被定义,那么就会使用__repr__来代替输出
注意:这俩方法的返回值必须是字符串,否则抛出异常
'''
print(format(s1,'nat'))
print(format(s1,'tna'))
print(format(s1,'tan'))
print(format(s1,'asfdasdffd'))%s和%r：
class B:
def __str__(self):
return 'str : class B'
def __repr__(self):
return 'repr : class B'
b=B()
print('%s'%b)
print('%r'%b)2、item系列
1）、__getitem__\__setitem__\__delitem__
class Foo:
def __init__(self,name):
self.name=name
def __getitem__(self, item):
print(self.__dict__[item])
def __setitem__(self, key, value):
self.__dict__[key]=value
def __delitem__(self, key):
print('del obj[key]时,我执行')
self.__dict__.pop(key)
def __delattr__(self, item):
print('del obj.key时,我执行')
self.__dict__.pop(item)
f1=Foo('sb')
f1['age']=18
f1['age1']=19
del f1.age1
del f1['age']
f1['name']='alex'
print(f1.__dict__)2、__del__
析构方法，当对象在内存中被释放时，自动触发执行。
注：此方法一般无须定义，因为Python是一门高级语言，程序员在使用时无需关心内存的分配和释放，因为此工作都是交给Python解释器来执行，所以，析构函数的调用是由解释器在进行垃圾回收时自动触发执行的。
简单示范：
class Foo:
def __del__(self):
print('执行我啦')
f1=Foo()
del f1
print('------->')
#输出结果
执行我啦
------->3、__new__
class A:
def __init__(self):
self.x = 1
print('in init function')
def __new__(cls, *args, **kwargs):
print('in new function')
return object.__new__(A)
a = A()
print(a.x)单例设计模式：
class Singleton:
def __new__(cls, *args, **kw):
if not hasattr(cls, '_instance'):
cls._instance = object.__new__(cls)
return cls._instance
one = Singleton()
two = Singleton()
two.a = 3
print(one.a)
# 3
# one和two完全相同,可以用id(), ==, is检测
print(id(one))
# 29097904
print(id(two))
# 29097904
print(one == two)
# True
print(one is two)4、__call__
对象后面加括号，触发执行。
注：构造方法的执行是由创建对象触发的，即：对象 = 类名() ；而对于 __call__ 方法的执行是由对象后加括号触发的，即：对象() 或者 类()()
class Foo:
def __init__(self):
pass
def __call__(self, *args, **kwargs):
print('__call__')
obj = Foo() # 执行 __init__
obj() # 执行 __call__5、with和__enter__,__exit__
with语句：
class A:
def __enter__(self):
print('before')
def __exit__(self, exc_type, exc_val, exc_tb):
print('after')
with A() as a:
print('123')with语句和init：
class A:
def __init__(self):
print('init')
def __enter__(self):
print('before')
def __exit__(self, exc_type, exc_val, exc_tb):
print('after')
with A() as a:
print('123')with和文件操作：
class Myfile:
def __init__(self,path,mode='r',encoding = 'utf-8'):
self.path = path
self.mode = mode
self.encoding = encoding
def __enter__(self):
self.f = open(self.path, mode=self.mode, encoding=self.encoding)
return self.f
def __exit__(self, exc_type, exc_val, exc_tb):
self.f.close()
with Myfile('file',mode='w') as f:
f.write('wahaha'with和pickle：
import pickle
class MyPickledump:
def __init__(self,path):
self.path = path
def __enter__(self):
self.f = open(self.path, mode='ab')
return self
def dump(self,content):
pickle.dump(content,self.f)
def __exit__(self, exc_type, exc_val, exc_tb):
self.f.close()
class Mypickleload:
def __init__(self,path):
self.path = path
def __enter__(self):
self.f = open(self.path, mode='rb')
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.f.close()
def load(self):
return pickle.load(self.f)
def loaditer(self):
while True:
try:
yield self.load()
except EOFError:
break
# with MyPickledump('file') as f:
# f.dump({1,2,3,4})
with Mypickleload('file') as f:
for item in f.loaditer():
print(item)with和pickle和iter：
import pickle
class MyPickledump:
def __init__(self,path):
self.path = path
def __enter__(self):
self.f = open(self.path, mode='ab')
return self
def dump(self,content):
pickle.dump(content,self.f)
def __exit__(self, exc_type, exc_val, exc_tb):
self.f.close()
class Mypickleload:
def __init__(self,path):
self.path = path
def __enter__(self):
self.f = open(self.path, mode='rb')
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.f.close()
def __iter__(self):
while True:
try:
yield pickle.load(self.f)
except EOFError:
break
# with MyPickledump('file') as f:
# f.dump({1,2,3,4})
with Mypickleload('file') as f:
for item in f:
print(item)6、__len__
class A:
def __init__(self):
self.a = 1
self.b = 2
def __len__(self):
return len(self.__dict__)
a = A()
print(len(a))7、__hash__
class A:
def __init__(self):
self.a = 1
self.b = 2
def __hash__(self):
return hash(str(self.a)+str(self.b))
a = A()
print(hash(a))8、__eq__
class A:
def __init__(self):
self.a = 1
self.b = 2
def __eq__(self,obj):
if self.a == obj.a and self.b == obj.b:
return True
a = A()
b = A()
print(a == b)纸牌游戏：
class FranchDeck:
ranks = [str(n) for n in range(2,11)] + list('JQKA')
suits = ['红心','方板','梅花','黑桃']
def __init__(self):
self._cards = [Card(rank,suit) for rank in FranchDeck.ranks
for suit in FranchDeck.suits]
def __len__(self):
return len(self._cards)
def __getitem__(self, item):
return self._cards[item]
deck = FranchDeck()
print(deck[0])
from random import choice
print(choice(deck))
print(choice(deck))纸牌游戏2：
class FranchDeck:
ranks = [str(n) for n in range(2,11)] + list('JQKA')
suits = ['红心','方板','梅花','黑桃']
def __init__(self):
self._cards = [Card(rank,suit) for rank in FranchDeck.ranks
for suit in FranchDeck.suits]
def __len__(self):
return len(self._cards)
def __getitem__(self, item):
return self._cards[item]
def __setitem__(self, key, value):
self._cards[key] = value
deck = FranchDeck()
print(deck[0])
from random import choice
print(choice(deck))
print(choice(deck))
from random import shuffle
shuffle(deck)
print(deck[:5])面试题：
class Person:
def __init__(self,name,age,sex):
self.name = name
self.age = age
self.sex = sex
def __hash__(self):
return hash(self.name+self.sex)
def __eq__(self, other):
if self.name == other.name and self.sex == other.sex:return True
p_lst = []
for i in range(84):
p_lst.append(Person('egon',i,'male'))
print(p_lst)
print(set(p_lst))
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