学习笔记，仅供参考，有错必纠

文章目录

• ​​python 学习高级篇​​

• ​​类对象的特殊方法之`__iter__()`和`__next__()`​​
• ​​类对象的特殊方法之`__add__()`和`__radd__()`​​

python 学习高级篇

# 支持多行输出
from IPython.core.interactiveshell import InteractiveShell 
InteractiveShell.ast_node_interactivity = 'all' #默认为'last'

类对象的特殊方法之​​__iter__()​​​和​​__next__()​​

L = [1, 2, 3, 4, 5]

for item in L:
    print(item)

1
2
3
4
5

for-in语句在默认情况下不能用于自定义类对象的实例对象

class MyClass(object):
    pass

for item in MyClass():  # TypeError: 'MyClass' object is not iterable
    print(item)

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-2-4128e49c4e9a> in <module>()
      2     pass
      3 
----> 4 for item in MyClass():  # TypeError: 'MyClass' object is not iterable
      5     print(item)


TypeError: 'MyClass' object is not iterable

class MyClass(object):
    def __init__(self):
        self.data = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.data > 5:
            raise StopIteration()
        else:
            self.data += 1
            return self.data

for item in MyClass():
    print(item)

1
2
3
4
5
6

类对象的特殊方法之​​__add__()​​​和​​__radd__()​​

标准算术运算符在默认情况下不能用于自定义类对象的实例对象

class MyClass1(object):
    pass

class MyClass2(object):
    pass

print(MyClass1() + MyClass2())

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-5-eff96f1ce3ef> in <module>()
      5     pass
      6 
----> 7 print(MyClass1() + MyClass2())


TypeError: unsupported operand type(s) for +: 'MyClass1' and 'MyClass2'

如果想让标准算术运算符可以用于自定义类对象的实例对象，必须在自定义类对象中实现标准算术运算符对应的以下特殊方法:

之所以可以使用加法和乘法运算符操作列表，是因为列表所对应的类对象​​list​​​中实现了​​+​​​和​​*​​对应的特殊方法;

之所以可以使用加法和乘法运算符操作字符串，是因为字符串所对应的类对象​​str​​​中实现了​​+​​​和​​*​​对应的特殊方法。

# 测试1
class C1(object):
    def __add__(self, other):
        print("特殊方法__add__被调用")
        return "xxx"
        # return NotImplemented

class C2(object):
    def __radd__(self, other):
        print("特殊方法__radd__被调用")
        return "yyy"
        # return NotImplemented

obj1 = C1()
obj2 = C2()

print(obj1 + obj2)

特殊方法__add__被调用
xxx

# 测试2
class C1(object):
    pass

class C2(object):
    def __radd__(self, other):
        print("特殊方法__radd__被调用")
        return "yyy"
        # return NotImplemented

obj1 = C1()
obj2 = C2()

print(obj1 + obj2)

特殊方法__radd__被调用
yyy

# 测试3
class C1(object):
    def __add__(self, other):
        print("特殊方法__add__被调用")
        return NotImplemented

class C2(object):
    def __radd__(self, other):
        print("特殊方法__radd__被调用")
        return "yyy"
        # return NotImplemented

obj1 = C1()
obj2 = C2()

print(obj1 + obj2)

特殊方法__add__被调用
特殊方法__radd__被调用
yyy