Joe's questions

我正在尝试使用 numpy.fill_diagonal()（如本答案所示）将数据框的对角线条目更改为 20,000。但是，当我运行下面的示例时，数据框中的对角线条目保持为零。我的问题是“为什么？”

请不要发布一些答案来展示如何使用 for 循环更改对角线条目。我可以自己更改对角线条目。我的问题是为什么下面的示例无法更改条目。如果我不明白为什么下面的示例失败，我就不能在任何代码中依赖 numpy.fill_diagonal()。我使用的是 numpy 版本 2.1.0 和 pandas 版本 2.2.2。

import numpy as np
import pandas as pd

nodes = ['A','B','C','D','E','F','G','H']
df_cap = pd.DataFrame(None, index=nodes, columns=nodes)

edges = {
    ('A', 'B'): 809, ('A', 'C'): 184, ('A', 'D'): 440, ('B', 'C'): 134, 
    ('B', 'E'): 277, ('B', 'F'): 138, ('C', 'D'): 194, ('C', 'F'): 144,
    ('C', 'G'): 139, ('D', 'E'): 190, ('D', 'G'): 284, ('E', 'F'): 100,
    ('E', 'H'): 281,('F', 'H'): 922,('G', 'F'): 123,('G', 'H'): 232
}

for i in nodes:
    for j in nodes:
        if (i,j) in edges:
            df_cap.loc[i,j] = edges[(i,j)]

nodes = nodes + ["Dummy"]


df_cap = df_cap.astype(float).fillna(0)
df_cap.loc["Dummy", :] = 0
df_cap.loc[:, "Dummy"] = 0
np.fill_diagonal(df_cap.values, 20000)

df_cap.loc["A", "Dummy"] = 20000
df_cap.loc["Dummy", "H"] = 20000
df_cap

在的文档randrange()中，它指出：

不应使用关键字参数，因为它们可能会以意想不到的方式被解释。例如，randrange(start=100)被解释为randrange(0, 100, 1)。

如果签名是random.randrange(start, stop[, step])，为什么不会randrange(start=100)引发错误，因为stop没有传递值？

为什么会randrange(start=100)被解释为randrange(0, 100, 1)？

我并不是想了解编写代码的人的设计选择，而是想了解这是如何实现的。我认为没有默认值的参数需要传递参数，否则会引发 TypeError。

这是一个代表

import urllib # to retrieve the file from the internet
from PIL import Image # to interpret the bytes as an image
import numpy as np # to work with arrays of numbers (the image is an array of pixels)
import matplotlib.pyplot as plt # for general plotting

# The URL for the file
url = r"https://upload.wikimedia.org/wikipedia/en/9/9d/The_Tilled_Field.jpg"

img = np.array(Image.open(urllib.request.urlopen(url)))

# Make a figure and axes
fig, ax = plt.subplots(figsize=(4.5, 6.4))

# Add the image to the axes
ax.imshow(img);

# Say where to put the ticks on the axes
ax.set_xticks(range(0,1300,100), minor=False)
ax.set_xticks(range(0,1300,20), minor=True)
ax.set_yticks(range(0,900,100), minor=False)
ax.set_yticks(range(0,900,20), minor=True)

# Add some gridlines
ax.grid(which='minor', color='grey');


# I want this figure to be inlayed inside the bigger figure
ax.imshow(img, extent=[400,528,200,290]);

我认为范围会使第二个ax.imshow图像放入第一个图像内，但事实并非如此。

如果我删除该行，它就会完全符合我的预期。但是当我使用这条线时，而不是在指定范围内绘制在上一张图像之上，它似乎创建了一个全新的绘图。

有谁知道我做错了什么？

我尝试在 Jupyter 实验室和 Jupyter 笔记本中运行此示例 ，并从终端运行脚本，在所有情况下它都是静态的 - 不是交互式的。path_editor.ipynbpath_editor.py

当我从终端运行脚本时，我收到消息：

QWidget::repaint: Recursive repaint detected
QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::end: Painter not active, aborted

我有 matplotlib 版本 3.8.4、Jupyter Lab 版本 4.1.8 和 Jupyter Notebook 版本 7.1.3。

这是该示例的代码（来自上面链接的网站）：

import matplotlib.pyplot as plt
import numpy as np

from matplotlib.backend_bases import MouseButton
from matplotlib.patches import PathPatch
from matplotlib.path import Path

fig, ax = plt.subplots()

pathdata = [
    (Path.MOVETO, (1.58, -2.57)),
    (Path.CURVE4, (0.35, -1.1)),
    (Path.CURVE4, (-1.75, 2.0)),
    (Path.CURVE4, (0.375, 2.0)),
    (Path.LINETO, (0.85, 1.15)),
    (Path.CURVE4, (2.2, 3.2)),
    (Path.CURVE4, (3, 0.05)),
    (Path.CURVE4, (2.0, -0.5)),
    (Path.CLOSEPOLY, (1.58, -2.57)),
]

codes, verts = zip(*pathdata)
path = Path(verts, codes)
patch = PathPatch(
    path, facecolor='green', edgecolor='yellow', alpha=0.5)
ax.add_patch(patch)


class PathInteractor:
    """
    A path editor.

    Press 't' to toggle vertex markers on and off.  When vertex markers are on,
    they can be dragged with the mouse.
    """

    showverts = True
    epsilon = 5  # max pixel distance to count as a vertex hit

    def __init__(self, pathpatch):

        self.ax = pathpatch.axes
        canvas = self.ax.figure.canvas
        self.pathpatch = pathpatch
        self.pathpatch.set_animated(True)

        x, y = zip(*self.pathpatch.get_path().vertices)

        self.line, = ax.plot(
            x, y, marker='o', markerfacecolor='r', animated=True)

        self._ind = None  # the active vertex

        canvas.mpl_connect('draw_event', self.on_draw)
        canvas.mpl_connect('button_press_event', self.on_button_press)
        canvas.mpl_connect('key_press_event', self.on_key_press)
        canvas.mpl_connect('button_release_event', self.on_button_release)
        canvas.mpl_connect('motion_notify_event', self.on_mouse_move)
        self.canvas = canvas

    def get_ind_under_point(self, event):
        """
        Return the index of the point closest to the event position or *None*
        if no point is within ``self.epsilon`` to the event position.
        """
        xy = self.pathpatch.get_path().vertices
        xyt = self.pathpatch.get_transform().transform(xy)  # to display coords
        xt, yt = xyt[:, 0], xyt[:, 1]
        d = np.sqrt((xt - event.x)**2 + (yt - event.y)**2)
        ind = d.argmin()
        return ind if d[ind] < self.epsilon else None

    def on_draw(self, event):
        """Callback for draws."""
        self.background = self.canvas.copy_from_bbox(self.ax.bbox)
        self.ax.draw_artist(self.pathpatch)
        self.ax.draw_artist(self.line)
        self.canvas.blit(self.ax.bbox)

    def on_button_press(self, event):
        """Callback for mouse button presses."""
        if (event.inaxes is None
                or event.button != MouseButton.LEFT
                or not self.showverts):
            return
        self._ind = self.get_ind_under_point(event)

    def on_button_release(self, event):
        """Callback for mouse button releases."""
        if (event.button != MouseButton.LEFT
                or not self.showverts):
            return
        self._ind = None

    def on_key_press(self, event):
        """Callback for key presses."""
        if not event.inaxes:
            return
        if event.key == 't':
            self.showverts = not self.showverts
            self.line.set_visible(self.showverts)
            if not self.showverts:
                self._ind = None
        self.canvas.draw()

    def on_mouse_move(self, event):
        """Callback for mouse movements."""
        if (self._ind is None
                or event.inaxes is None
                or event.button != MouseButton.LEFT
                or not self.showverts):
            return

        vertices = self.pathpatch.get_path().vertices

        vertices[self._ind] = event.xdata, event.ydata
        self.line.set_data(zip(*vertices))

        self.canvas.restore_region(self.background)
        self.ax.draw_artist(self.pathpatch)
        self.ax.draw_artist(self.line)
        self.canvas.blit(self.ax.bbox)


interactor = PathInteractor(patch)
ax.set_title('drag vertices to update path')
ax.set_xlim(-3, 4)
ax.set_ylim(-3, 4)

plt.show()

有什么办法可以让这个例子发挥作用吗？

编辑

安装后ipympl，将笔记本分成两个单元（一个用于导入，第二个用于其他所有内容），然后将其放在%matplotlib ipympl第二个单元的顶部，我现在收到以下错误消息：

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\IPython\core\formatters.py:974, in MimeBundleFormatter.__call__(self, obj, include, exclude)
    971     method = get_real_method(obj, self.print_method)
    973     if method is not None:
--> 974         return method(include=include, exclude=exclude)
    975     return None
    976 else:

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\ipympl\backend_nbagg.py:336, in Canvas._repr_mimebundle_(self, **kwargs)
    333     plaintext = plaintext[:110] + '…'
    335 buf = io.BytesIO()
--> 336 self.figure.savefig(buf, format='png', dpi='figure')
    338 base64_image = b64encode(buf.getvalue()).decode('utf-8')
    339 self._data_url = f'data:image/png;base64,{base64_image}'

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\figure.py:3390, in Figure.savefig(self, fname, transparent, **kwargs)
   3388     for ax in self.axes:
   3389         _recursively_make_axes_transparent(stack, ax)
-> 3390 self.canvas.print_figure(fname, **kwargs)

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backend_bases.py:2193, in FigureCanvasBase.print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
   2189 try:
   2190     # _get_renderer may change the figure dpi (as vector formats
   2191     # force the figure dpi to 72), so we need to set it again here.
   2192     with cbook._setattr_cm(self.figure, dpi=dpi):
-> 2193         result = print_method(
   2194             filename,
   2195             facecolor=facecolor,
   2196             edgecolor=edgecolor,
   2197             orientation=orientation,
   2198             bbox_inches_restore=_bbox_inches_restore,
   2199             **kwargs)
   2200 finally:
   2201     if bbox_inches and restore_bbox:

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backend_bases.py:2043, in FigureCanvasBase._switch_canvas_and_return_print_method.<locals>.<lambda>(*args, **kwargs)
   2039     optional_kws = {  # Passed by print_figure for other renderers.
   2040         "dpi", "facecolor", "edgecolor", "orientation",
   2041         "bbox_inches_restore"}
   2042     skip = optional_kws - {*inspect.signature(meth).parameters}
-> 2043     print_method = functools.wraps(meth)(lambda *args, **kwargs: meth(
   2044         *args, **{k: v for k, v in kwargs.items() if k not in skip}))
   2045 else:  # Let third-parties do as they see fit.
   2046     print_method = meth

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backends\backend_agg.py:497, in FigureCanvasAgg.print_png(self, filename_or_obj, metadata, pil_kwargs)
    450 def print_png(self, filename_or_obj, *, metadata=None, pil_kwargs=None):
    451     """
    452     Write the figure to a PNG file.
    453 
   (...)
    495         *metadata*, including the default 'Software' key.
    496     """
--> 497     self._print_pil(filename_or_obj, "png", pil_kwargs, metadata)

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backends\backend_agg.py:445, in FigureCanvasAgg._print_pil(self, filename_or_obj, fmt, pil_kwargs, metadata)
    440 def _print_pil(self, filename_or_obj, fmt, pil_kwargs, metadata=None):
    441     """
    442     Draw the canvas, then save it using `.image.imsave` (to which
    443     *pil_kwargs* and *metadata* are forwarded).
    444     """
--> 445     FigureCanvasAgg.draw(self)
    446     mpl.image.imsave(
    447         filename_or_obj, self.buffer_rgba(), format=fmt, origin="upper",
    448         dpi=self.figure.dpi, metadata=metadata, pil_kwargs=pil_kwargs)

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backends\backend_agg.py:388, in FigureCanvasAgg.draw(self)
    385 # Acquire a lock on the shared font cache.
    386 with (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
    387       else nullcontext()):
--> 388     self.figure.draw(self.renderer)
    389     # A GUI class may be need to update a window using this draw, so
    390     # don't forget to call the superclass.
    391     super().draw()

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\artist.py:95, in _finalize_rasterization.<locals>.draw_wrapper(artist, renderer, *args, **kwargs)
     93 @wraps(draw)
     94 def draw_wrapper(artist, renderer, *args, **kwargs):
---> 95     result = draw(artist, renderer, *args, **kwargs)
     96     if renderer._rasterizing:
     97         renderer.stop_rasterizing()

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\artist.py:72, in allow_rasterization.<locals>.draw_wrapper(artist, renderer)
     69     if artist.get_agg_filter() is not None:
     70         renderer.start_filter()
---> 72     return draw(artist, renderer)
     73 finally:
     74     if artist.get_agg_filter() is not None:

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\figure.py:3164, in Figure.draw(self, renderer)
   3161 finally:
   3162     self.stale = False
-> 3164 DrawEvent("draw_event", self.canvas, renderer)._process()

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backend_bases.py:1271, in Event._process(self)
   1269 def _process(self):
   1270     """Process this event on ``self.canvas``, then unset ``guiEvent``."""
-> 1271     self.canvas.callbacks.process(self.name, self)
   1272     self._guiEvent_deleted = True

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\cbook.py:303, in CallbackRegistry.process(self, s, *args, **kwargs)
    301 except Exception as exc:
    302     if self.exception_handler is not None:
--> 303         self.exception_handler(exc)
    304     else:
    305         raise

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\cbook.py:87, in _exception_printer(exc)
     85 def _exception_printer(exc):
     86     if _get_running_interactive_framework() in ["headless", None]:
---> 87         raise exc
     88     else:
     89         traceback.print_exc()

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\cbook.py:298, in CallbackRegistry.process(self, s, *args, **kwargs)
    296 if func is not None:
    297     try:
--> 298         func(*args, **kwargs)
    299     # this does not capture KeyboardInterrupt, SystemExit,
    300     # and GeneratorExit
    301     except Exception as exc:

Cell In[2], line 73, in PathInteractor.on_draw(self, event)
     71 self.ax.draw_artist(self.pathpatch)
     72 self.ax.draw_artist(self.line)
---> 73 self.canvas.blit(self.ax.bbox)

File ~\AppData\Local\anaconda3\envs\joe_env\lib\site-packages\matplotlib\backends\backend_webagg_core.py:195, in FigureCanvasWebAggCore.blit(self, bbox)
    193 def blit(self, bbox=None):
    194     self._png_is_old = True
--> 195     self.manager.refresh_all()

AttributeError: 'NoneType' object has no attribute 'refresh_all'

我熟悉使用requirements.txtor安装依赖项environment.yml，但我只在这些文件中见过语法，例如some_package>=1.2.3.

当依赖项用大括号列出时，这意味着什么，如下所示：

pytest = "^6.2.5"
coverage = {extras = ["toml"], version = "^5.5"}
safety = "^1.10.3"
mypy = "^0.910"
typeguard = "^2.12.1"
xdoctest = {extras = ["colors"], version = "^0.15.5"}
Sphinx = "^4.1.2"
sphinx-autobuild = "^2021.3.14"

以及如何安装这些依赖项？

尝试通过将文件视为requirements.txt或来安装它们，分别environment.yml抛出ERROR: Invalid requirement或CondaValueError: invalid package specification。

我试图理解Python中的文件IO，使用不同的打开模式，以及读取和写入同一文件对象（只是自学）。

我对以下代码感到惊讶（这只是我的探索）：

with open('blah.txt', 'w') as f:

    # create a file with 13 characters
    f.write("hello, world!")


with open('blah.txt', 'r+') as f:

    for i in range(5):

        # write one character
        f.write(str(i))

        # then print current position and next 3 characters
        print(f"{f.tell()}: ", f"{f.read(3)}")


with open('blah.txt', 'r') as f:

    # look at how the file was modified
    print(f.read())

哪个输出：

1:  ell
14:  
15:  
16:  
17:  
0ello, world!1234

正如我所料，第一个字符被 覆盖0，然后接下来读取的 3 个字符是ell，但我预计 会1被写入o，hello然后接下来的 3 个字符读取为, w。

我正在阅读此处的文档，但我没有看到它在哪里解释了我观察到的行为。

看起来，无论大小如何，第一次读取都会查找文件末尾。

任何人都可以提供文档中解释这一点的链接吗？

我尝试在此网站上搜索类似的问题，但是虽然有很多与阅读相关的问题，但我发现没有一个提到这种行为。

更新

经过更多探索后，发现不是第一次read写入文件末尾，而是第二次写入。同样，我不确定为什么，这就是为什么我希望在文档中找到解释这种行为的地方。

这是我对上面代码的更改，表明它不是第一次读取：

with open('blah.txt', 'w') as f:

    # create a file with 13 characters
    f.write("hello, world!")


with open('blah.txt', 'r+') as f:

    for i in range(3):

        # write one character
        f.write(str(i))

        # then print current position and next 3 characters
        print(f"{f.tell()}: ", f"{f.read(3)}")
        print(f"{f.tell()}: ", f"{f.read(3)}")


with open('blah.txt', 'r') as f:

    # look at how the file was modified
    print(f.read())

哪个输出：

1:  ell
4:  o, 
14:  
14:  
15:  
15:  
0ello, world!12```