我想知道__init__和__call__方法之间的区别。
例如:
class test:
def __init__(self):
self.a = 10
def __call__(self):
b = 20
我想知道__init__和__call__方法之间的区别。
例如:
class test:
def __init__(self):
self.a = 10
def __call__(self):
b = 20
当前回答
第一个用于初始化新创建的对象,并接收用于初始化的参数:
class Foo:
def __init__(self, a, b, c):
# ...
x = Foo(1, 2, 3) # __init__
第二部分实现函数调用操作符。
class Foo:
def __call__(self, a, b, c):
# ...
x = Foo()
x(1, 2, 3) # __call__
其他回答
因此,当你创建任何类的实例并初始化实例变量时,__init__也会被调用。
例子:
class User:
def __init__(self,first_n,last_n,age):
self.first_n = first_n
self.last_n = last_n
self.age = age
user1 = User("Jhone","Wrick","40")
当你像调用其他函数一样调用对象时,会调用__call__。
例子:
class USER:
def __call__(self,arg):
"todo here"
print(f"I am in __call__ with arg : {arg} ")
user1=USER()
user1("One") #calling the object user1 and that's gonna call __call__ dunder functions
在Python中,函数是一级对象,这意味着:函数引用可以在输入中传递给其他函数和/或方法,并在它们内部执行。
类的实例(又名对象),可以像函数一样对待:将它们传递给其他方法/函数并调用它们。为了实现这一点,__call__类函数必须特殊化。
Def __call__(self, [args…]) 它接受可变数量的参数作为输入。假设x是类x的实例,x.__call__(1,2)类似于将x(1,2)或实例本身作为函数调用。
在Python中,__init__()被正确地定义为类构造函数(以及__del__()是类析构函数)。因此,在__init__()和__call__()之间有一个净区别:第一个创建Class的实例,第二个使该实例可以像函数一样被调用,而不会影响对象本身的生命周期(即__call__不影响构建/销毁生命周期),但它可以修改其内部状态(如下所示)。
的例子。
class Stuff(object):
def __init__(self, x, y, range):
super(Stuff, self).__init__()
self.x = x
self.y = y
self.range = range
def __call__(self, x, y):
self.x = x
self.y = y
print '__call__ with (%d,%d)' % (self.x, self.y)
def __del__(self):
del self.x
del self.y
del self.range
>>> s = Stuff(1, 2, 3)
>>> s.x
1
>>> s(7, 8)
__call__ with (7,8)
>>> s.x
7
方法用于使对象像函数一样工作。
>>> class A:
... def __init__(self):
... print "From init ... "
...
>>> a = A()
From init ...
>>> a()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: A instance has no __call__ method
<*There is no __call__ method so it doesn't act like function and throws error.*>
>>>
>>> class B:
... def __init__(self):
... print "From init ... "
... def __call__(self):
... print "From call it is a function ... "
...
>>> b = B()
From init ...
>>> b()
From call it is a function...
>>>
<* __call__ method made object "b" to act like function *>
我们也可以把它传递给一个类变量。
class B:
a = A()
def __init__(self):
print "From init ... "
>>> class A:
... def __init__(self):
... print "From init ... "
...
>>> a = A()
From init ...
>>> a()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: A instance has no __call__ method
>>>
>>> class B:
... def __init__(self):
... print "From init ... "
... def __call__(self):
... print "From call ... "
...
>>> b = B()
From init ...
>>> b()
From call ...
>>>
__call__允许返回任意值,而__init__作为构造函数隐式返回类的实例。正如其他答案正确指出的那样,__init__只被调用一次,而__call__有可能被调用多次,以防初始化的实例被赋值给中间变量。
>>> class Test:
... def __init__(self):
... return 'Hello'
...
>>> Test()
Traceback (most recent call last):
File "<console>", line 1, in <module>
TypeError: __init__() should return None, not 'str'
>>> class Test2:
... def __call__(self):
... return 'Hello'
...
>>> Test2()()
'Hello'
>>>
>>> Test2()()
'Hello'
>>>