重载赋值运算符 [英] Overloading assignment operator

问题描述

我想用Python编写应用程序中的一些公式。用户

应该可以写出类似的东西


A = B * C


其中A，B ，C是一些包装类的实例。重载*是没有问题但是我不能超载A的赋值。我明白这是因为Python的本质，但有一个解决方法

这个？

所有我感兴趣的是一个干净的语法来编写我的应用程序脚本。任何想法都很受欢迎。


问候，

Achim

解决方案

Achim Domma写道：

我想用Python编写我的应用程序中的一些公式。用户

应该可以写出类似的东西


A = B * C


其中A，B ，C是一些包装类的实例。重载*是没有问题但是我不能超载A的赋值。我明白这是因为Python的本质，但有一个解决方法

这个？

>> class D（dict）：

.... def __setitem __（self，key，value）：

.... print key，" ;< - "，value

.... dict .__ setitem __（自我，钥匙，价值）

....

>> namespace = D（B = 42，C = 24）
exec" A = B * C在命名空间

A< - 1008


Peter

1月23日下午12:24，Achim Domma< d ... @ procoders.netwrote：

我想用Python编写应用程序中的一些公式。用户

应该可以写出类似的东西


A = B * C


其中A，B ，C是一些包装类的实例。重载*是没有问题但是我不能超载A的赋值。我明白这是因为Python的本质，但有一个解决方法

这个？

所有我感兴趣的是一个干净的语法来编写我的应用程序脚本。任何想法都很受欢迎。


问候，

Achim

简单选项：您如何使用''<< =< =''而不是''=''（通过定义__ilshift__来定义
）？这给你：


A<< = B * C


（看起来有点像注入B的结果时间C进入A）


更复杂的选项：将表达式/赋值解析器嵌入到你的应用程序的
中。你可以使用一些带有pyparsing的示例来获得跳跃（可以在线检查这些 http://pyparsing.wikispaces.com/Examples - 查看fourFn.py和

simpleArith.py）。 />

- Paul

Achim Domma写道：

我想用Python在我的应用程序中编写一些公式。用户

应该可以写出类似的东西


A = B * C


其中A，B ，C是一些包装类的实例。重载*是没有问题但是我不能超载A的赋值。我明白这是因为Python的本质，但有一个解决方法

这个？

所有我感兴趣的是一个干净的语法来编写我的应用程序脚本。任何想法都很受欢迎。
非常欢迎。

你确定你甚至需要这样做吗？

>> C类：

.... def __init __（self，x） ：

.... self.x = x

.... def __mul __（自我，其他）：

....返回C（self.x * other.x）

....

>>结果= C（2）* C（3）
打印结果

< __ main __。位于0x402e13ec的C实例>

>> result.x

6


-

Erik Max Francis&& ma*@alcyone.com && http://www.alcyone.com/max/

美国加利福尼亚州圣何塞市&& 37 20 N 121 53 W&& AIM，Y！M erikmaxfrancis

生活是无法入睡的事情。

- Fran Lebowitz

Hi,

I want to use Python to script some formulas in my application. The user
should be able to write something like

A = B * C

where A,B,C are instances of some wrapper classes. Overloading * is no
problem but I cannot overload the assignment of A. I understand that
this is due to the nature of Python, but is there a trick to work around
this?
All I''m interested in is a clean syntax to script my app. Any ideas are
very welcome.

regards,
Achim

解决方案

Achim Domma wrote:

I want to use Python to script some formulas in my application. The user
should be able to write something like

A = B * C

where A,B,C are instances of some wrapper classes. Overloading * is no
problem but I cannot overload the assignment of A. I understand that
this is due to the nature of Python, but is there a trick to work around
this?

>>class D(dict):

.... def __setitem__(self, key, value):
.... print key, "<--", value
.... dict.__setitem__(self, key, value)
....

>>namespace = D(B=42, C=24)
exec "A = B * C" in namespace

A <-- 1008

Peter

On Jan 23, 12:24 pm, Achim Domma <[e-mail]:

Hi,

I want to use Python to script some formulas in my application. The user
should be able to write something like

A = B * C

where A,B,C are instances of some wrapper classes. Overloading * is no
problem but I cannot overload the assignment of A. I understand that
this is due to the nature of Python, but is there a trick to work around
this?
All I''m interested in is a clean syntax to script my app. Any ideas are
very welcome.

regards,
Achim

Simple option: how do you feel about using ''<<='' instead of ''='' (by
defining __ilshift__)? This gives you:

A <<= B * C

(looks sort of like "injecting" the result of B times C into A)

More complicated option: embed an expression/assignment parser into
your app. You can get a jump on this using some of the examples that
come with pyparsing (can check these out online at
http://pyparsing.wikispaces.com/Examples - look at fourFn.py and
simpleArith.py).

-- Paul

Achim Domma wrote:

I want to use Python to script some formulas in my application. The user
should be able to write something like

A = B * C

where A,B,C are instances of some wrapper classes. Overloading * is no
problem but I cannot overload the assignment of A. I understand that
this is due to the nature of Python, but is there a trick to work around
this?
All I''m interested in is a clean syntax to script my app. Any ideas are
very welcome.

Are you sure you even need to do that?

>>class C:

.... def __init__(self, x):
.... self.x = x
.... def __mul__(self, other):
.... return C(self.x*other.x)
....

>>result = C(2)*C(3)
print result

<__main__.C instance at 0x402e13ec>

>>result.x

6

--
Erik Max Francis && ma*@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis
Life is something to do when you can''t get to sleep.
-- Fran Lebowitz

这篇关于重载赋值运算符的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！