Question

让我们采用以下代码，定义算术运算符对象（标记）：

RegularExpressionValidator

我希望将运算符分组到某处，以便我可以迭代它们或检查成员资格。由于我稍后会添加很多其他内容，因此我只想将它们添加到一个地方，而不是两个（实现运营商但忘记将其添加到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可能引起微妙的错误）。我尝试过像

这样的事情

operators

和类似，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operators = (PLUS = Operator(0), MIN = Operator(0), ...)定义：

dict

这样可以正常工作，但这意味着任何时候我想要使用单个运算符，我必须将其称为例如operators = dict( PLUS=Operator(0), MIN=Operator(0), ... )，而不是更短更清晰的operators['PLUS']。我可以忍受哪些，但我想知道是否存在更好的解决方案。

Answer 1

您可以使用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

Answer 2

您可以执行以下操作：

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

为什么不让操作员将自己添加到您的组中？

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，这也适用于模块级变量中的集合：

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)

如果必须将运算符添加到多个组中的一个组，则使表示该组的集合将运算符添加到用于初始化运算符的必需参数：

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)

Python：将对象组合在一起

3 个答案: