我正在尝试从 numpy 页面运行这个关于 histogram2d 的非常简单的示例:
https://numpy.org/doc/stable/reference/ generated/numpy.histogram2d.html.
from matplotlib.image import NonUniformImage
import matplotlib.pyplot as plt
xedges = [0, 1, 3, 5]
yedges = [0, 2, 3, 4, 6]
x = np.random.normal(2, 1, 100)
y = np.random.normal(1, 1, 100)
H, xedges, yedges = np.histogram2d(x, y, bins=(xedges, yedges))
H = H.T
fig = plt.figure(figsize=(7, 3))
ax = fig.add_subplot(131, title='imshow: square bins')
plt.imshow(H, interpolation='nearest', origin='lower',extent=[xedges[0], xedges[-1], yedges[0], yedges[-1]])
ax = fig.add_subplot(132, title='pcolormesh: actual edges',aspect='equal')
X, Y = np.meshgrid(xedges, yedges)
ax.pcolormesh(X, Y, H)
ax = fig.add_subplot(133, title='NonUniformImage: interpolated',aspect='equal', xlim=xedges[[0, -1]], ylim=yedges[[0, -1]])
im = NonUniformImage(ax, interpolation='bilinear')
xcenters = (xedges[:-1] + xedges[1:]) / 2
ycenters = (yedges[:-1] + yedges[1:]) / 2
im.set_data(xcenters,ycenters,H)
ax.images.append(im)
plt.show()
通过按照示例运行此代码,我收到错误
无法解压不可迭代的 NoneType 对象
当我运行 ax.images.append(im) 行时,就会发生这种情况。
有谁知道为什么会发生这种情况?
尝试从 numpy 网站运行示例,但未按预期工作。
完整的错误消息是:
TypeError Traceback (most recent call last)
File ~\anaconda3\lib\site-packages\IPython\core\formatters.py:339, in BaseFormatter.__call__(self, obj)
337 pass
338 else:
--> 339 return printer(obj)
340 # Finally look for special method names
341 method = get_real_method(obj, self.print_method)
File ~\anaconda3\lib\site-packages\IPython\core\pylabtools.py:151, in print_figure(fig, fmt, bbox_inches, base64, **kwargs)
148 from matplotlib.backend_bases import FigureCanvasBase
149 FigureCanvasBase(fig)
--> 151 fig.canvas.print_figure(bytes_io, **kw)
152 data = bytes_io.getvalue()
153 if fmt == 'svg':
File ~\anaconda3\lib\site-packages\matplotlib\backend_bases.py:2299, in FigureCanvasBase.print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
2297 if bbox_inches:
2298 if bbox_inches == "tight":
-> 2299 bbox_inches = self.figure.get_tightbbox(
2300 renderer, bbox_extra_artists=bbox_extra_artists)
2301 if pad_inches is None:
2302 pad_inches = rcParams['savefig.pad_inches']
File ~\anaconda3\lib\site-packages\matplotlib\figure.py:1632, in FigureBase.get_tightbbox(self, renderer, bbox_extra_artists)
1629 artists = bbox_extra_artists
1631 for a in artists:
-> 1632 bbox = a.get_tightbbox(renderer)
1633 if bbox is not None and (bbox.width != 0 or bbox.height != 0):
1634 bb.append(bbox)
File ~\anaconda3\lib\site-packages\matplotlib\axes\_base.py:4666, in _AxesBase.get_tightbbox(self, renderer, call_axes_locator, bbox_extra_artists, for_layout_only)
4662 if np.all(clip_extent.extents == axbbox.extents):
4663 # clip extent is inside the Axes bbox so don't check
4664 # this artist
4665 continue
-> 4666 bbox = a.get_tightbbox(renderer)
4667 if (bbox is not None
4668 and 0 < bbox.width < np.inf
4669 and 0 < bbox.height < np.inf):
4670 bb.append(bbox)
File ~\anaconda3\lib\site-packages\matplotlib\artist.py:355, in Artist.get_tightbbox(self, renderer)
340 def get_tightbbox(self, renderer):
341 """
342 Like `.Artist.get_window_extent`, but includes any clipping.
343
(...)
353 The enclosing bounding box (in figure pixel coordinates).
354 """
--> 355 bbox = self.get_window_extent(renderer)
356 if self.get_clip_on():
357 clip_box = self.get_clip_box()
File ~\anaconda3\lib\site-packages\matplotlib\image.py:943, in AxesImage.get_window_extent(self, renderer)
942 def get_window_extent(self, renderer=None):
--> 943 x0, x1, y0, y1 = self._extent
944 bbox = Bbox.from_extents([x0, y0, x1, y1])
945 return bbox.transformed(self.axes.transData)
TypeError: cannot unpack non-iterable NoneType object
<Figure size 504x216 with 3 Axes>
错误发生在
append
调用的深处,并且似乎涉及尝试获取有关绘图窗口的信息。如果我注释掉 append
行,并继续到 plt.show()
,生成的图像看起来像示例,除了第三个图像是空白的。
我在 Windows 中测试了这个
QtConsole
;我不知道这种情况是否会带来问题append
。我不认为这是你的代码副本的问题。
解决方案是将参数
extent=(0,6,0,6)
添加到 NonUniformImage
函数中。
im = NonUniformImage(ax, interpolation="bilinear", extent=(0, 6, 0, 6))
当我尝试实现示例代码时,我遇到了完全相同的问题。我怀疑这可能与版本有关,因此我用谷歌搜索了当前
NonUniformImage
函数的文档并进行比较以找到差异:https://matplotlib.org/stable/gallery/images_contours_and_fields/image_nonuniform.html
xedges = [0, 1, 3, 5]
yedges = [0, 2, 3, 4, 6]
x = np.random.normal(2, 1, 100)
y = np.random.normal(1, 1, 100)
H, xedges, yedges = np.histogram2d(x, y, bins=(xedges, yedges))
# Histogram does not follow Cartesian convention (see Notes),
# therefore transpose H for visualization purposes.
H = H.T
fig = plt.figure(figsize=(7, 3))
ax = fig.add_subplot(131, title='imshow: square bins')
plt.imshow(H, interpolation='nearest', origin='lower',extent=[xedges[0], xedges[-1], yedges[0], yedges[-1]])
ax = fig.add_subplot(132, title='pcolormesh: actual edges',aspect='equal')
X, Y = np.meshgrid(xedges, yedges)
ax.pcolormesh(X, Y, H)
ax = fig.add_subplot(133, title='NonUniformImage: interpolated', aspect='equal', xlim=xedges[[0, -1]], ylim=yedges[[0, -1]])
im = NonUniformImage(ax, interpolation="bilinear", extent=(0, 6, 0, 6))
xcenters = (xedges[:-1] + xedges[1:]) / 2
ycenters = (yedges[:-1] + yedges[1:]) / 2
im.set_data(xcenters, ycenters, H)
ax.add_image(im)