的Python：组合对象在一起

Question

让我们以下面的一段代码，定义算术运算符对象（标记）：

class Operator: 
    def __init__(self, precedence): 
     self.precedence = precedence 

PLUS = Operator(0) 
UPLUS = Operator(10) 
MIN = Operator(0) 
UMIN = Operator(10) 
MULT = Operator(20) 
operators = PLUS, UPLUS, MIN, UMIN, MULT 

我想运营商在某处被分组，这样我可以在他们重复或检查的成员。因为我稍后会添加很多其他人，所以我想只能将它们添加到一个地方，而不是两个（实现一个操作员，但忘记将其添加到operators可能导致微妙的错误）。我试过类似

operators = (PLUS = Operator(0), MIN = Operator(0), ...) 

和类似的，但这显然不是一个有效的Python语句。

我目前使用的解决方案是一个dict定义：

operators = dict(
    PLUS=Operator(0), 
    MIN=Operator(0), 
    ... 
) 

该工程确定，但它意味着任何时候我想用一个单一运营商的工作，我必须把它称为例如operators['PLUS']，而不是更简短更清晰的​​。我可以住在哪里，但我想知道是否存在更好的解决方案。

Answer 1

为什么不能有运营商自己添加到您的组？

class Operator: 
    all = [] 
    def __init__(self, precedence): 
     self.precedence = precedence 
     self.all.append(self) # Modifies the class variable, as we haven't 
           # introduced an instance variable with that name. 

PLUS = Operator(0) 
UPLUS = Operator(10) 
MIN = Operator(0) 
UMIN = Operator(10) 
MULT = Operator(20) 

# Freeze the collection of Operators 
Operator.all = tuple(Operator.all) 

当然，这也与收集工作在模块级变量：

operators = [] 

class Operator: 
    def __init__(self, precedence): 
     self.precedence = precedence 
     operators.append(self) 

PLUS = Operator(0) 
UPLUS = Operator(10) 
MIN = Operator(0) 
UMIN = Operator(10) 
MULT = Operator(20) 

# Freeze the collection of Operators 
operators = tuple(operators) 

如果运营商必须加入几组之一，使收集代表组添加运营商为运营商的初始化必要参数：

u_operators = [] 
non_u_operators = [] 

class Operator: 
    def __init__(self, precedence, group): 
     self.precedence = precedence 
     group.append(self) 

PLUS = Operator(0, non_u_operators) 
UPLUS = Operator(10, u_operators) 
MIN = Operator(0, non_u_operators) 
UMIN = Operator(10, u_operators) 
MULT = Operator(20, non_u_operators) 

# Freeze the collections of Operators 
non_u_operators = tuple(non_u_operators) 
u_operators = tuple(u_operators) 

Answer 2

你可以这样做：

class Operator: 
    def __init__(self, precedence): 
     self.precedence = precedence 
Operator.PLUS = Operator(0) 
Operator.UPLUS = Operator(10) 
Operator.MIN = Operator(0) 
Operator.UMIN = Operator(10) 
Operator.MULT = Operator(20) 

[o for o in dir(Operator) if not o.startswith('__')] 

Answer 3

你可以使用一个Enum：

from enum import Enum 

class Operator: 
    def __init__(self, precedence): 
     self.precedence = precedence 

    def __str__(self): 
     return "Operator: prec={}".format(self.precedence) 

class Operators(Enum): 
    PLUS = Operator(0) 
    UPLUS = Operator(10) 
    MIN = Operator(0) 
    UMIN = Operator(10) 
    MULT = Operator(20) 

p = Operators.PLUS 
print(p)  # Operators.PLUS 
print(p.name) # PLUS 
print(p.value) # Operator: prec=0