运行和调试时输出不同

Question

我想要打印树。因此，问题在于我的RUN输出与DEBUG的输出有所不同，并且在创建DEBUG实例时似乎正在调用__str__（在DEBUG时变量self.__visited已被填充）。我在PyCharm工作。

这是用于查找属性的类...

class ListTree:
    def __attrnames(self,obj,indent):
        spaces=' '*(indent+1)
        result=''
        for attr in sorted(obj.__dict__):
            if attr.startswith('__') and attr.endswith('__'):
                result+=spaces+f'{attr}\n'
            else:
                result+=spaces+f'{attr}={getattr(obj,attr)}\n'
        return result

    def __listclass(self, aClass, indent):
        dots = '.' * indent
        if aClass in self.__visited:
            return '\n{0}<Class {1}:, address {2}: (see above)>\n'.format(
                dots,
                aClass.__name__,
                id(aClass))
        else:
            self.__visited[aClass] = True
            here = self.__attrnames(aClass, indent)
            above = ''
            for super in aClass.__bases__:
                above += self.__listclass(super, indent + 4)
            return '\n{0}<Class {1}, address {2}:\n{3}{4}{5}>\n'.format(
                dots,
                aClass.__name__,
                id(aClass),
                here, above,
                dots)

    def __str__(self):
        print('hello world from __str__')
        self.__visited = {}
        here = self.__attrnames(self, 0)
        above = self.__listclass(self.__class__, 4)
        return '<Instance of {0}, address {1}:\n{2}{3}>'.format(
            self.__class__.__name__,
            id(self),
            here, above)

这些是要打印的类

class Super():
    def __init__(self):
        self.data1 = 'spam'

    def ham(self):
        pass

class Sub(Super, ListTree):
    def __init__(self):
        Super.__init__(self)
        self.data2 = 'eggs'
        self.data3 = 42

    def spam(self):
        pass

instanse = Sub()
print(instanse)

来自RUN的输出是：

hello world from __str__
<Instance of Sub, address 140389925768448:
 _ListTree__visited={}
 data1=spam
 data2=eggs
 data3=42

....<Class Sub, address 28451744:
     __doc__
     __init__
     __module__
     spam=<function Sub.spam at 0x7faf13a1b670>

........<Class Super, address 28450800:
         __dict__
         __doc__
         __init__
         __module__
         __weakref__
         ham=<function Super.ham at 0x7faf13a1b550>

............<Class object, address 9435264:

DEBUG的输出是：

...
...(lots of repeating hello world from __str__)
...
hello world from __str__
hello world from __str__
hello world from __str__
hello world from __str__
hello world from __str__
hello world from __str__
hello world from __str__
<Instance of Sub, address 140359544124464:
 _ListTree__visited={<class '__main__.Sub'>: True, <class '__main__.Super'>: True, <class 'object'>: True, <class '__main__.ListTree'>: True}
 data1=spam
 data2=eggs
 data3=42

....<Class Sub:, address 41729904: (see above)>
>

Answer 1

PyCharm，以及更全局的IntelliJ IDEA IDE，重复地调用本地变量上的字符串转换器以在调试面板中显示其值。

在Python中，此字符串转换器为str，它调用对象的__str__方法。如果您的__str__方法有副作用（例如在stdout上输出内容），那么这种副作用会发生很多次（至少每次您在调试器中按Next按钮时，有时会更多）。