Python继承导致非法属性错误

Question

我有下面一个类 vuln.py

from reportlab.graphics.shapes import Drawing, String, Rect

class vuln(Drawing):
    def __init__(self, width=300, height=150, report_type=None, *args, **kw):
        Drawing.__init__(self, width, height, *args, **kw)
        self.report_type = report_type

    def print_report(self):
        print self.report_type

并调用程序rep.py

import vuln

obj = vuln.vuln(report_type="abc")
obj.print_report()

执行后报错，

Traceback (most recent call last):
  File "rep.py", line 3, in <module>
    obj = vuln.vuln(report_type="abc")
  File "/data/support/vuln.py", line 5, in __init__
    self.report_type = report_type
  File "/usr/lib64/python2.6/site-packages/reportlab/graphics/shapes.py", line 359, in __setattr__
    validateSetattr(self,attr,value)    #from reportlab.lib.attrmap
  File "/usr/lib64/python2.6/site-packages/reportlab/lib/attrmap.py", line 118, in validateSetattr
    raise AttributeError, "Illegal attribute '%s' in class %s" % (name, obj.__class__.__name__)
AttributeError: Illegal attribute 'report_type' in class vuln

请帮忙知道是什么错误。

Answer 1

长话短说，他们的开发人员正在给您带来这种痛苦，并在做他们不应该在 Python 中做的事情。幸运的是它是开源的。您正在使用的 API 动态检查从 Shape 继承的类的属性，或者如他们在 /reportlab/graphics/shapes.py, line 359 中所说:

if shapeChecking:
        """This adds the ability to check every attribute assignment as it is made.
        It slows down shapes but is a big help when developing. It does not
        get defined if rl_config.shapeChecking = 0"""
        def __setattr__(self, attr, value):
            """By default we verify.  This could be off
            in some parallel base classes."""
            validateSetattr(self,attr,value)    #from reportlab.lib.attrmap

继续挖掘代码和 attrmap source code 的第 99 行您可以看到导致问题的原因:

def validateSetattr(obj,name,value):
    '''validate setattr(obj,name,value)'''
    if rl_config.shapeChecking:
        map = obj._attrMap
        if map and name[0]!= '_':
            #we always allow the inherited values; they cannot
            #be checked until draw time.
            if isinstance(value, DerivedValue):
                #let it through
                pass
            else:            
                try:
                    validate = map[name].validate
                    if not validate(value):
                        raise AttributeError("Illegal assignment of '%s' to '%s' in class %s" % (value, name, obj.__class__.__name__))
                except KeyError:
                    raise AttributeError("Illegal attribute '%s' in class %s" % (name, obj.__class__.__name__))
    obj.__dict__[name] = value

请注意，他们不检查以 _ 或 __ 开头的属性，pythonists 使用这些属性来指示“私有(private)”变量；因此，您可以按如下方式修复您的代码:

from reportlab.graphics.shapes import Drawing, String, Rect

class vuln(Drawing):
    def __init__(self, width=300, height=150, report_type=None, *args, **kw):
        Drawing.__init__(self, width, height, *args, **kw)
        self._report_type = report_type

    def print_report(self):
        print self._report_type

然后一切都应该正常工作。