AttributeError：“复合”对象在vpython.py中没有属性“_origin”

Question

需要做些什么来解决这个问题？

在https://www.glowscript.org/#/user/murray.garth/folder/Public/program/Eyeballs，我找到了一个GlowScript示例，我试图将其用作python3脚本。

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我将标题修改为

#https://www.glowscript.org/#/user/murray.garth/folder/Public/program/Eyeballs
#GlowScript 2.1 VPython
from vpython import *

并将真假引用改为大写。

正在运行

python3 eyeballs.py 

启动静态图像

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然后给出错误消息：

compound event return
compound event return
compound event return
Traceback (most recent call last):
  File "eyeballs.py", line 39, in <module>
    world_pos = Head.compound_to_world( vRightEye.pos )
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/vpython/vpython.py", line 1553, in compound_to_world
    v = v-self._origin
AttributeError: 'compound' object has no attribute '_origin'

根据https://www.glowscript.org/docs/VPythonDocs/compound.html，compound_to_world的语法是：

world_pos = c.compound_to_world(v) 

似乎没问题。对我来说。

环境是macports python3。

python3 --version
Python 3.7.4

我安装了vpython

pip install vpython
pip --version
pip 18.1 from /opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pip (python 3.7)

Answer 1

这是一次艰难的考验。关于堆栈溢出的python，大约有120万个问题。如果你在寻找

[python]"object has no attribute" 

你得到了大约12066的结果。所以这可能就是为什么这个问题没有得到足够的关注。

根据https://www.glowscript.org/docs/VPythonDocs/compound.html，我用一个较小的例子尝试了这个问题

from vpython import *

handle = cylinder( size=vec(1,.2,.2),color=vec(0.72,0.42,0) )
head = box( size=vec(.2,.6,.2), pos=vec(1.1,0,0),color=color.gray(.6) )

hammer = compound([handle, head])
hammer.axis = vec(1,1,0)

world_pos = hammer.compound_to_world(hammer.axis) 

给出问题中提到的错误：

compound event return
Traceback (most recent call last):
  File "hammer.py", line 10, in <module>
    print (hammer.origin)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/vpython/vpython.py", line 1536, in origin
    return self._origin
AttributeError: 'compound' object has no attribute '_origin'

vpython.py的相关源代码行是：

@property
def origin(self):
    return self._origin

@origin.setter
def origin(self,value): # compound origin cannot be reset
   if not self._constructing:
      raise AttributeError('The compound "origin" attribute is read-only; change "pos" instead.')
   self._origin = value

def world_to_compound(self, v):
        v = v-self._pos
        x_axis = self._axis.hat
        y_axis = self._up.hat
        z_axis = x_axis.cross(y_axis)
        ox = self._size0.x/self._size.x # _size0 is the original size
        oy = self._size0.y/self._size.y
        oz = self._size0.z/self._size.z
        return self._origin + vector(v.dot(x_axis)*ox, v.dot(y_axis)*oy, v.dot(z_axis)*oz)

def compound_to_world(self, v):
        v = v-self._origin
        x_axis = self._axis.hat
        y_axis = self._up.hat
        z_axis = x_axis.cross(y_axis)
        ox = self._size.x/self._size0.x # _size0 is the original size
        oy = self._size.y/self._size0.y
        oz = self._size.z/self._size0.z
        return self._pos + v.x*ox*x_axis + v.y*oy*y_axis + v.z*oz*z_axis

实际上，在构造函数后面的几行构造函数没有设置任何起源。因此，添加一个默认的原点：

class compound(standardAttributes):
    compound_idx = 0 # same numbering scheme as in GlowScript

    def __init__(self, objList, **args):
        self._origin = vector(0,0,0)

使语法错误消失。

from vpython import *

handle = cylinder( size=vec(1,.2,.2),                   color=vec(0.72,0.42,0) )

head = box( size=vec(.2,.6,.2), pos=vec(1.1,0,0),              color=color.gray(.6) )

hammer = compound([handle, head])
hammer.axis = vec(1,1,0)

print (hammer.origin)

world_pos = hammer.compound_to_world(hammer.axis)
print (world_pos)

然后给出结果：

compound event return
<0, 0, 0>
<0.6, 1.41421, 0>

eyeballs.py代码的工作方式与预期的一样：

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我不知道在那里报告这个错误，但我发布了发送给vpython-user组的消息。

Answer 2

谢谢您报告这个bug，我将在vpython存储库中报告这个问题。正如您所说，解决办法是指定一个起源。