Question

我想计算在类FUNCTION中执行一个特定功能CLASS.的次数，我试图通过在类counting_function_execution中定义一个全局变量并增加它来增加次数每次执行该函数：

class CLASS:
    global counting_function_execution 
    counting_function_execution  = 0

    def __init__(self,name):
        self.name = name

    def FUNCTION(self):
        print("Hi " + self.name)
        print("This function was already excecuted ", counting_function_execution, " number of times.")
        counting_function_execution += 1

但是，当我这样做时：

test = CLASS("Fred")
test.FUNCTION()
test.FUNCTION()

我得到：

---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-104-dc8f3ae96700> in <module>()
      1 test = CLASS("Fred")
----> 2 test.say_hi()

<ipython-input-100-d0166079c633> in say_hi(self)
      8     def say_hi(self):
      9         print("Hi " + self.name)
---> 10         print("This function was already excecuted ", counting_function_execution, " number of times.")
     11         counting_function_execution += 1
     12 

UnboundLocalError: local variable 'counting_function_execution' referenced before assignment

Answer 1

问题在于，在函数CLASS.FUNCTION中，您不是在引用类变量counting_function_execution，而是在引用另一个具有相同名称的局部变量。
这就是为什么“在分配之前先引用”错误的原因，因为在初始化之前先引用了该局部变量。

要引用正确的变量，可以使用self.counting_function_execution（实例的变量）或CLASS.counting_function_execution（类的静态变量）

Answer 2

counting_function_execution是一个类变量。如果要从类的实例访问它，请使用self.counting_function_execution。如果您想从类本身访问它，请使用x.counting_function_execution，其中x是类的名称（在这种情况下为CLASS）

两种方式均可用于您的示例

Answer 3

Henry，您在这里得到了一些令人困惑的答案，因为它并不是100％清楚您想要什么，尤其是在您有多个类实例的情况下。如果要对所有变量进行一次计数，则需要从实例中引用类变量，例如：

class CLASS:
    # static class counting_function_execution 
    counting_function_execution  = 0

    def __init__(self,name):
        self.name = name

    def FUNCTION(self):
        print("Hi " + self.name)
        print("This function was already excecuted ", self.counting_function_execution, " number of times.")
        self.__class__.counting_function_execution += 1

c = CLASS("mark")
c.FUNCTION()      # 0
c.FUNCTION()      # 1

d = CLASS("john")
d.FUNCTION()      # 2
d.FUNCTION()      # 3

print(CLASS.counting_function_execution) #4

这将打印0-3，最后CLASS.counting_function_execution等于4。

如果您改为使用self.counting_function_execution += 1，则每个实例将获得其自己的计数，而CLASS.counting_function_execution的末尾将为零，因为您从未实际对其进行递增。

无论哪种方式，您都可以避免使用global变量，这是一个奖励。

Answer 4

如果要计算每个类的执行量，则可以在类之外定义一些内容：

counting_function_execution = 0

def count_func(func):
    def decorator_count(self, *args, **kwargs):
        global counting_function_execution
        counting_function_execution += 1
        print(counting_function_execution)
        return func(self, *args, **kwargs)
    return decorator_count


class CLASS:
    # global counting_function_execution 
    # counting_function_execution  = 0

    def __init__(self,name):
        self.name = name

    @count_func
    def FUNCTION(self):
        print("Hi " + self.name)
        #print("This function was already excecuted ", self.counting_function_execution, " number of times.")

如果您要计算每个实例的执行量，则只需在引用它时添加self，即self.counting_function_execution。

class CLASS:
    # global counting_function_execution 
    counting_function_execution  = 0

    def __init__(self,name):
        self.name = name

    def FUNCTION(self):
        print("Hi " + self.name)
        print("This function was already excecuted ", self.counting_function_execution, " number of times.")
        self.counting_function_execution += 1

计算执行某类函数的次数

4 个答案: