Using ipympl logic inside python shell or ipython?

还没有人认领这个 Issue。

I have a class that inherits from the `ipywidgets.widgets.VBox` and adds a `figure.canvas` instance of a matplotlib figure to its children like so:

```python
import matplotlib.pyplot as plt
from ipywidgets import widgets

plt.ioff()

class MyVis(widgets.VBox):
def __init__(self):
super().__init__()
self.fig = plt.figure()
self.children = [self.fig.canvas]

m = MyVis()
```

This works fine when I use this class within jupyter notebooks using the `%matplotlib widget` magic before executing the above code.
When executed within ipython I get
`TraitError: Element of the 'children' trait of a MyVis instance must be a Widget, but a value of was specified.`
since of course `ipympl` and its magic are not active.

Since I also want to have unit-tests for this class (and others that make use of this class) using `pytest`, it would be nice to get around this problem.
Can I enable the `ipympl` way of handling figures somehow in the python shell (similar to using the `%matplotlib widget` magic in the notebook) that would allow my tests to run?

从 MyVis 示例开始，在 IPython 中重现 TraitError，然后将其与使用 `%matplotlib widget` magic 的 notebook 设置进行比较。检查 matplotlib canvas 的选择方式，并确定什么样的测试设置可以让 pytest 测试用例在 Jupyter 之外使用兼容的 widget canvas；当该类能够在不出现 Tk canvas 错误的情况下被实例化和测试时，即表示完成。

由索引模型根据 Issue 内容生成。