change context manager for temporary auto-reverted `figure.layout`

Instead of

fig.layout.showlegend = False
fig.write_image('plot.pdf')
fig.layout.showlegend = True

it would be nice to write

from plotly.express import plotly_patch  # or similar

with plotly_patch(fig.layout, showlegend=False):
    fig.write_image('plot.pdf')

I tried

from unittest.mock import patch

with patch.dict(fig.layout, showlegend=False):
    fig.write_image('plot.pdf')

which unfortunately doesn't correctly restore the previous value but tries to delete the patched keys which is undesired behavior and raises AttributeError to boot:

   1906 """Unpatch the dict."""
   1907 if self._original is not None:
-> 1908     self._unpatch_dict()
...
   1934 keys = list(in_dict)
   1935 for key in keys:
-> 1936     del in_dict[key]

AttributeError: __delitem__

Related

Found this forum post where such a context manager was welcomed.

issue 中没有指定源文件或测试。首先定位 figure layout 的变更和恢复行为，然后检查 context manager 如何保留现有值，并在 fig.write_image('plot.pdf'); 之后恢复这些值；done 应包含对临时 showlegend 变更的覆盖，同时不删除 layout 键。