Python中“__eq__”与“is”与“==”的区别
有多种方法可以比较Python中任何类型的对象。 Python具有“ == ”运算符、“ is ”运算符和“ __eq__ ”dunder 方法，用于比较一个类的两个对象或自定义比较。本文解释了上述三个运算符以及它们之间的区别。
==运算符
“==”运算符比较两个对象的值或相等性，而Python的“is”运算符检查两个变量是否指向内存中的同一个对象。
示例 1：
Python3
# lists initialization
x = [1, 2]
y = [1, 2]
z = y
# comparisons
print("x == y : ", x == y)
print("z == y : ", z == y)
# location in memory
print("Location of x is ", id(x))
print("Location of y is ", id(y))
print("Location of z is ", id(z))Python3
class Student:
def __init__(self, name):
self.name = name
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh == shivansh : ", (divyansh == shivansh))Python3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh == shivansh : ", (divyansh == shivansh))Python3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh is shivansh : ", (divyansh is shivansh))Python3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = divyansh
print("divyansh is shivansh : ", (divyansh is shivansh))Python3
x = [1, 2]
y = [1, 2]
z = y
print("x is y : ", x is y)
print("z is y : ", z is y)
print("Location of x is ", id(x))
print("Location of y is ", id(y))
print("Location of z is ", id(z))x == y : True
z == y : True
Location of x is 140169895643144
Location of y is 140169895642952
Location of z is 140169895642952
示例 2：
蟒蛇3
class Student:
def __init__(self, name):
self.name = name
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh == shivansh : ", (divyansh == shivansh))
divyansh == shivansh : False
在上面的例子中，我们应该得到一个输出True ，但我们收到的输出是False 。这是因为，对于用户定义类的对象，我们需要指定我们将如何比较它们。我们创建的Student对象不知道两个学生相等的标准是什么，也许他们有相同的属性“名称”，也许他们有一堆关于他们的其他特征。什么需要相同才能让我们说一个 Student 对象与另一个 Student 相同。好吧，这就是我们将通过实现一个名为__eq__的方法自己指定的内容。这是dunder方法之一 在Python中。它允许我们覆盖Python中“ == ”运算符的基本功能。
示例 3：
蟒蛇3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh == shivansh : ", (divyansh == shivansh))
divyansh == shivansh : True
实现这个 dunder 方法，在 Student 类的两个对象之间使用“ == ”运算符并获得准确的值比较，现在如果我将其切换为 ' is '运算符，情况将会有所不同。
示例 4：
蟒蛇3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = Student("Divyansh")
print("divyansh is shivansh : ", (divyansh is shivansh))
divyansh is shivansh : False
在上面的代码片段中，我们收到False作为输出，这是因为divyansh将与shivansh不同，尽管这些对象具有相同的值。然而，它们具有不同的存储位置，即它们是不同且独特的对象，可以在任何时间点独立地改变它们的属性。
示例 5：
蟒蛇3
class Student:
def __init__(self, name):
self.name = name
def __eq__(self, other):
if isinstance(other, Student):
if other.name == self.name:
return True
return False
divyansh = Student("Divyansh")
shivansh = divyansh
print("divyansh is shivansh : ", (divyansh is shivansh))
divyansh is shivansh : True
现在在上面的示例中，输出为True，这是因为 shivansh 指向与 divyansh 指向的同一 Student 对象。
“是”运算符
“is”运算符比较两个对象的身份。这里我们比较对象本身。
示例 6：
蟒蛇3
x = [1, 2]
y = [1, 2]
z = y
print("x is y : ", x is y)
print("z is y : ", z is y)
print("Location of x is ", id(x))
print("Location of y is ", id(y))
print("Location of z is ", id(z))
x is y : False
z is y : True
Location of x is 139987316430856
Location of y is 139987316430664
Location of z is 139987316430664
在上面的示例中，即使 x 和 y 具有相同的值，它们也会将它们存储在内存中的不同位置。所以很明显，即使对象在值方面相同，它们在内存中的位置实际上是不同的。我们还看到在上面的片段中z is y给出True ，这是因为这些对象实际上是相同的，即上面 y 的位置和 z 的位置完全相同。