Python 運算符重載 · PythonGuru 中文系列教程

# Python 運算符重載 > 原文： [https://thepythonguru.com/python-operator-overloading/](https://thepythonguru.com/python-operator-overloading/) * * * 于 2020 年 1 月 7 日更新 * * * 您已經看到可以使用`+`運算符添加數字，并同時連接字符串。這是可能的，因為`int`類和`str`類都重載了`+`運算符。運算符實際上是在各個類中定義的方法。運算符的定義方法稱為運算符重載。例如：要對自定義對象使用`+`運算符，您需要定義一個名為`__add__`的方法。讓我們舉個例子來更好地理解 ```py import math class Circle: ? ? def __init__(self, radius): ? ? ? ? self.__radius = radius ? ? def setRadius(self, radius): ? ? ? ? self.__radius = radius ? ? def getRadius(self): ? ? ? ? return self.__radius ? ? def area(self): ? ? ? ? return math.pi * self.__radius ** 2 ? ? def __add__(self, another_circle): ? ? ? ? return Circle( self.__radius + another_circle.__radius ) c1 = Circle(4) print(c1.getRadius()) c2 = Circle(5) print(c2.getRadius()) c3 = c1 + c2 # This became possible because we have overloaded + operator by adding a ? ?method named __add__ print(c3.getRadius()) ``` **預期輸出**： ```py 4 5 9 ``` ```py import math class Circle: def __init__(self, radius): self.__radius = radius def setRadius(self, radius): self.__radius = radius def getRadius(self): return self.__radius def area(self): return math.pi * self.__radius ** 2 def __add__(self, another_circle): return Circle( self.__radius + another_circle.__radius ) c1 = Circle(4) print(c1.getRadius()) c2 = Circle(5) print(c2.getRadius()) c3 = c1 + c2 # This became possible because we have overloaded + operator by adding a method named __add__ print(c3.getRadius()) ``` 在上面的示例中，我們添加了`__add__()`方法，該方法允許使用`+`運算符添加兩個圓形對象。在`__add__()`方法內部，我們正在創建一個新對象并將其返回給調用者。 Python 還有許多其他特殊方法，例如`__add__()`，請參見下面的列表。 | 運算符 | 函數 | 方法說明 | | --- | --- | --- | | `+` | `__add__(self, other)` | 加法 | | `*` | `__mul__(self, other)` | 乘法 | | `-` | `__sub__(self, other)` | 減法 | | `%` | `__mod__(self, other)` | 余數 | | `/` | `__truediv__(self, other)` | 除法 | | `<` | `__lt__(self, other)` | 小于 | | `<=` | `__le__(self, other)` | 小于或等于 | | `==` | `__eq__(self, other)` | 等于 | | `!=` | `__ne__(self, other)` | 不等于 | | `>` | `__gt__(self, other)` | 大于 | `>=`，`__ge__(self, other)`，大于或等于`[index]`，`__getitem__(self, index)`，索引運算符`in`，`__contains__(self, value)`，檢查成員資格`len`，`__len__(self)`，元素數`str`，`__str__(self)`的字符串表示形式下面的程序使用上面提到的一些函數來重載運算符。 ```py import math class Circle: ? ? def __init__(self, radius): ? ? ? ? self.__radius = radius ? ? def setRadius(self, radius): ? ? ? ? self.__radius = radius ? ? def getRadius(self): ? ? ? ? return self.__radius ? ? def area(self): ? ? ? ? return math.pi * self.__radius ** 2 ? ? def __add__(self, another_circle): ? ? ? ? return Circle( self.__radius + another_circle.__radius ) ? ? def __gt__(self, another_circle): ? ? ? ? return self.__radius > another_circle.__radius ? ? def __lt__(self, another_circle): ? ? ? ? return self.__radius < another_circle.__radius ? ? def __str__(self): ? ? ? ? return "Circle with radius " + str(self.__radius) c1 = Circle(4) print(c1.getRadius()) c2 = Circle(5) print(c2.getRadius()) c3 = c1 + c2 print(c3.getRadius()) print( c3 > c2) # Became possible because we have added __gt__ method print( c1 < c2) # Became possible because we have added __lt__ method print(c3) # Became possible because we have added __str__ method ``` **預期輸出**： ```py 4 5 9 True True Circle with radius 9 ``` ```py import math class Circle: def __init__(self, radius): self.__radius = radius def setRadius(self, radius): self.__radius = radius def getRadius(self): return self.__radius def area(self): return math.pi * self.__radius ** 2 def __add__(self, another_circle): return Circle( self.__radius + another_circle.__radius ) def __gt__(self, another_circle): return self.__radius > another_circle.__radius def __lt__(self, another_circle): return self.__radius < another_circle.__radius def __str__(self): return "Circle with radius " + str(self.__radius) c1 = Circle(4) print(c1.getRadius()) c2 = Circle(5) print(c2.getRadius()) c3 = c1 + c2 print(c3.getRadius()) print( c3 > c2) # Became possible because we have added __gt__ method print( c1 < c2) # Became possible because we have added __lt__ method print(c3) # Became possible because we have added __str__ method ``` 下一課是[繼承和多態](/python-inheritance-and-polymorphism/)。 * * * * * *