从 `matplotlib.patches.RegularPolygon` 继承在实例化时会产生 `ValueError`

Question

我正在尝试从matplotlib.patches.RegularPolygon 派生一个类。 近期目标是为matplotlib.patches.Circle 和matplotlib.patches.RegularPolygon （它们的某些属性不同）提供一个稍微统一的API，然后我可以在我的应用程序的其余部分使用它。由于到目前为止所有代码都是为Circle 编写的，因此修改RegularPolygon 的属性是有意义的。

但是，由于某种原因，参数没有正确传递——至少这是我迄今为止最好的解释。我可以使用一些指针为什么会这样。盯着源码（link）看了很久，没看到（可能是找错地方了）。

MWE

import matplotlib

class RegularPolygon(matplotlib.patches.RegularPolygon):
    def __init__(self, *args, **kwargs):
        super(matplotlib.patches.RegularPolygon, self).__init__(*args, **kwargs)

RegularPolygon((0.,0.), 5, radius=5, orientation=0)

错误信息

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-1189a0acbaf3> in <module>()
----> 1 RegularPolygon((0.,0.), 5, radius=5, orientation=0)

<ipython-input-3-3cc2c77e24bf> in __init__(self, *args, **kwargs)
      6
      7     def __init__(self, *args, **kwargs):
----> 8         super(matplotlib.patches.RegularPolygon, self).__init__(*args, **kwargs)

/home/paul/.virtualenvs/base2/local/lib/python2.7/site-packages/matplotlib/patches.pyc in __init__(self, edgecolor, facecolor, color, linewidth, linestyle, antialiased, hatch, fill, capstyle, joinstyle, **kwargs)
     93             self.set_color(color)
     94         else:
---> 95             self.set_edgecolor(edgecolor)
     96             self.set_facecolor(facecolor)
     97         # unscaled dashes.  Needed to scale dash patterns by lw

/home/paul/.virtualenvs/base2/local/lib/python2.7/site-packages/matplotlib/patches.pyc in set_edgecolor(self, color)
    282         """
    283         self._original_edgecolor = color
--> 284         self._set_edgecolor(color)
    285
    286     def set_ec(self, color):

/home/paul/.virtualenvs/base2/local/lib/python2.7/site-packages/matplotlib/patches.pyc in _set_edgecolor(self, color)
    270                 set_hatch_color = False
    271
--> 272         self._edgecolor = colors.to_rgba(color, self._alpha)
    273         if set_hatch_color:
    274             self._hatch_color = self._edgecolor

/home/paul/.virtualenvs/base2/local/lib/python2.7/site-packages/matplotlib/colors.pyc in to_rgba(c, alpha)
    132         rgba = _colors_full_map.cache[c, alpha]
    133     except (KeyError, TypeError):  # Not in cache, or unhashable.
--> 134         rgba = _to_rgba_no_colorcycle(c, alpha)
    135         try:
    136             _colors_full_map.cache[c, alpha] = rgba

/home/paul/.virtualenvs/base2/local/lib/python2.7/site-packages/matplotlib/colors.pyc in _to_rgba_no_colorcycle(c, alpha)
    187     c = tuple(c.astype(float))
    188     if len(c) not in [3, 4]:
--> 189         raise ValueError("RGBA sequence should have length 3 or 4")
    190     if len(c) == 3 and alpha is None:
    191         alpha = 1

ValueError: RGBA sequence should have length 3 or 4

Answer 1

使用

super(matplotlib.patches.RegularPolygon, self).__init__()

您调用了matplotlib.patches.RegularPolygon 的父级的init 函数。但是，您确实需要调用 matplotlib.patches.RegularPolygon 本身的 init。

我还建议不要为子类艺术家使用相同的名称，因为这可能会在这里增加混乱。

你有的选择

• 旧式

  import matplotlib
  
  class MyRegularPolygon(matplotlib.patches.RegularPolygon):
      def __init__(self, *args, **kwargs):
          matplotlib.patches.RegularPolygon.__init__(self, *args, **kwargs)
  
  r = MyRegularPolygon((0.,0.), 5, radius=5, orientation=0)
  

• 新样式（py2 & 3）

  import matplotlib
  
  class MyRegularPolygon(matplotlib.patches.RegularPolygon):
      def __init__(self, *args, **kwargs):
          super(MyRegularPolygon, self).__init__(*args, **kwargs)
  
  r = MyRegularPolygon((0.,0.), 5, radius=5, orientation=0)
  

• 新样式（仅 py3）

  import matplotlib
  
  class MyRegularPolygon(matplotlib.patches.RegularPolygon):
      def __init__(self, *args, **kwargs):
          super().__init__(*args, **kwargs)
  
  r = MyRegularPolygon((0.,0.), 5, radius=5, orientation=0)
  

我建议阅读What does 'super' do in Python? 以了解super 的一些解释。