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

[janosh]

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.

[alexcjohnson]

For completeness, another way to approach this is to copy the figure and modify the copy:

fig_static = go.Figure(fig)
fig_static.layout.showlegend = False
fig_static.write_image('plot.pdf')

This is a deep copy, including all data arrays, so not optimal performance for large figures. So yeah, I can certainly see the appeal of a context manager. I almost wonder if we could use update_layout and the other related methods like update_traces, update_xaxes... directly as the context managers:

with fig.update_layout(showlegend=False):
    fig.write_image('plot.pdf')

The pitfall I see with this API is that because the return value of fig.update_* is itself a figure already, there's no way to know it was called as part of a with statement, so something like:

fig = px.bar(...)
fig.update_layout(title_text="...")
fig.update_layout(showlegend=False)
with fig:
    fig.write_image('plot.pdf')
fig.show()

would have the result of reverting exactly the last update_* call when the with exits, which could be confusing. Also if you tried to chain several of these within the with call (with fig.update_layout(...).update_traces(...) and such) only the last one would be reverted when you leave the context. Incidentally the built-in open has similar issues but since there's nothing to chain there it's not really a problem in practice.

So if that seems like too big a downside we could make a new set of methods like fig.patch_layout that are designed to ONLY be used in a context manager but otherwise work exactly like fig.update_*

[janosh]

Here's what a minimal implementation might look like janosh/pymatviz#88. Probably not how plotly will do it but works for me and might be useful as a stopgap measure.