Question

在Python中进行练习时，我试图将变量传递给类的对象，并且该变量具有类的函数名称，但出现错误，没有出现跟随错误...

class testing():
    def __init__(self, name):
        print('This is From INIT of testing calss...')
        self.name = name

    def good(self):
        print('Hello {} Good things of the day'.format(self.name))

    def bad(self):
        print('Hello {} Bad things of the day'.format(self.name))

ts = testing('Pranit')
ch = str(input('Enter choice : good or bad :'))
ts.ch()

output error

C:\Users\pranit>python "C:\Users\pranit\Music\Python Only\FunPractice.py"
This is From INIT of testing calss...
Enter choice : good or bad :good
Traceback (most recent call last):
  File "C:\Users\pranit\Music\Python Only\FunPractice.py", line 15, in <module>
    ts.ch()
AttributeError: 'testing' object has no attribute 'ch'

C:\Users\pranit>

Answer 1

通常，解决方案是getattr(obj, name[, default=None)：

ts = testing('Pranit')
ch = input('Enter choice : good or bad :')
method = getattr(ts, ch, None)
if method:
    method()

但是在这种情况下（基于用户输入选择函数或方法）（出于安全原因）最好在客户端代码中明确映射允许的函数/方法：

ts = testing('Pranit')
allowed = {"good": ts.good, "bad": ts.bad}
ch = input('Enter choice : good or bad :')
method = allowed.get(ch, None)
if method:
    method()

或直接在类中（取决于谁负责了解此处允许使用哪些方法）：

# XXX Python naming conventions: class names should be CamelCased
class Testing():
    def __init__(self, name):
        print('This is From INIT of testing calss...')
        self.name = name

    def good(self):
        print('Hello {} Good things of the day'.format(self.name))

    def bad(self):
        print('Hello {} Bad things of the day'.format(self.name))

    ALLOWED = {"good": good, "bad": bad}

    def handle(self, choice):
       if choice not in self.ALLOWED:
           raise ValueError("'%s' is not a valid choice" % choice)
       return self.ALLOWED[choice][self]

Answer 2

您的课程只有一个属性：name和2个方法good()和bad()。因此，当您调用ts.ch()时会收到错误消息，因为您正在调用的方法ch()不存在。

您应该使用参数来定义方法的优缺点：

class testing():
    def __init__(self, name):
        print('This is From INIT of testing calss...')
        self.name = name

    def good(self):
        print('Hello {} Good things of the day'.format(self.name))

    def bad(self):
        print('Hello {} Bad things of the day'.format(self.name))

    def good_or_bad(self, param):
        # Param is either good or bad
        if param.lower() == "good":
            self.good()
        else:
            self.bad()

然后将ts.ch()替换为ts.good_or_bad(ch)。

将变量作为函数传递给对象时出错。在Python 3.7.0pyt

2 个答案: