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[Doc]: How to replicate behaviour of plt.gca(projection=...)? #20770
Description
Documentation Link
Problem
In version 3.4, passing keyword arguments to plt.gca() was deprecated. I was previously using plt.gca(projection='polar') to:
- Check if a polar projection axes exists, and if so return it
- If not, create a new axes with a polar projection
Looking at the documentation (https://matplotlib.org/stable/users/whats_new.html#changes-to-behavior-of-axes-creation-methods-gca-add-axes-add-subplot) it's not clear to me how to replicate this behaviour however. In pseudo-code I think what I want to do is:
if len(pyplot_axes):
if plt.gca().name != 'polar':
raise RuntimeError('Axes isn't polar projection')
else:
return plt.gca()
else:
return plt.subplot(projection='polar')The only thing I don't know how to get is a list of pyplot axes (pyplot_axes above). I looked at https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.html and didn't see anything, but perhaps there's another page I'm missing?
Suggested improvement
Add a clear description to the changelog (https://matplotlib.org/stable/users/whats_new.html#changes-to-behavior-of-axes-creation-methods-gca-add-axes-add-subplot) showing how to write code to reproduce plt.gca(projection=...).
Matplotlib Version
3.4.2
Matplotlib documentation version
3.4.2
Activity
anntzer commentedon Jul 31, 2021
I guess you are looking for is something like
if plt.get_fignums() and plt.gcf().axes? (get_fignums()will tell you if there's any pyplot figures around, and if there's one around you want to check if they already have any axes)jklymak commentedon Jul 31, 2021
Do we remember when this came in. I'm pretty sure we discussed this issue.
jklymak commentedon Aug 1, 2021
OK, this was #19153 and had a pretty long deprecation message, if I understand correctly. Was the deprecation message not showing up for
plt.gca()?@dsantsby, can you explain more your use case here? I guess I can see that one might organize one's axes this way, but it seems very ad-hoc to create a new polar axes unless one already exists, and in that case use the existing axes. Over all we are really trying to move away from state-based thinking, and this is a pretty extreme example.
dstansby commentedon Aug 1, 2021
The deprecation message is showing up for
plt.gca(), but it doesn't explain how to replicate the behaviour ofplt.gca(projection=...). I've copied the message at the bottom of this comment.My use case is a plot method in another library, which when called with no specified Axes I want to:
The reason I can't use
plt.gca()for step one is it will create a new Axes with a non-polar projection, and it's not then possible to change the projection after creating the Axes. #20773 seems to fix this.This is fair, but there's nothing in the what's new changelog entry explaining this or discouraging users. So I think there should either be a clear explanation to this effect explaining why
plt.gca(projection=...)is discouraged, or some clear instructions on how to replicate the behaviour ofplt.gca(projection=...).anntzer commentedon Sep 2, 2021
@dstansby I'll close this, as #20773 was superseded by #20783 which should(?) be sufficient and has been merged, but feel free to reopen or PR more docs if you disagree.
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