为什么说我的班级没有属性？

Question

here's my code:

class Regex:
    def __init__(self: 'Regex',
                    value: object =None, child: list =None, child2: list = None):  
        """node with value and any nummber of children"""
        list_of_regex = [0,1,2,'e','|','.','*']
        self.value = value
        if self.value not in list_of_regex:
                raise Exception
        if not child:
            self.child = []
        if not child2:
            self.child2 = []
        else:
            self.child = child[:]
            self.child = child2[:]

    def __repr__(self: 'Regex') -> str:
        return ('Regex(' + repr(self.value) + ', ' +
                        repr(self.child) + ', ' + repr(self.child2) + ')') 

when i input the following in my python shell:

>>>Regex(1,[1])

the output is:

    Traceback (most recent call last):
  File "C:\Program Files (x86)\Wing IDE 101 5.0\src\debug\tserver\_sandbox.py", line 1,     in <module>
    # Used internally for debug sandbox under external interpreter
  File "C:\Program Files (x86)\Wing IDE 101 5.0\src\debug\tserver\_sandbox.py", line 19,      in __repr__
builtins.AttributeError: 'Regex' object has no attribute 'child'

I'm not sure why it tells me that my class doesn't have the attribute 'child'. Look what happens when i try these two different calls.

>>>c = Regex(1)
>>>c.child
[]

>>>c = Regex(1,[1])
>>>c.child
Traceback (most recent call last):
File "<string>", line 1, in <fragment>
builtins.AttributeError: 'Regex' object has no attribute 'child'

what's wrong with the code?

Answer 1

    if not child:
        self.child = []
    if not child2:
        self.child2 = []
    else:
        self.child = child[:]
        self.child = child2[:]

The else block here is linked to the second if . It has no connection to the first if . That means if child is specified and child2 is not, the second if block is the only one that triggers, and child isn't set.

Also,

        self.child = child2[:]

you probably wanted to set the child2 attribute here.