Repository navigation
[Bug]: Secondary axis does not support Transform as functions #25691
Description
Bug summary
The documentation for secondary_[xy]axis claims to accept a Transform for the functions parameter.
However, the checks in set_functions do not accept Transform:
matplotlib/lib/matplotlib/axes/_secondary_axes.py
Lines 147 to 158 in 3f4d4c1
and any usage of the internal attribute seems to assume a tuple of callables:
matplotlib/lib/matplotlib/axes/_secondary_axes.py
Lines 193 to 194 in 3f4d4c1
Both this documentation and the checks have been in the code since it was added in #11859.
Code for reproduction
import matplotlib.pyplot as plt
from matplotlib.transforms import IdentityTransform
fig, ax = plt.subplots()
secax = ax.secondary_xaxis('top', functions=IdentityTransform)
# OR:
secax = ax.secondary_xaxis('top', functions=IdentityTransform())
# OR:
secax = ax.secondary_xaxis('top', functions=(IdentityTransform, IdentityTransform))
# OR:
secax = ax.secondary_xaxis('top', functions=(IdentityTransform(), IdentityTransform()))Actual outcome
With a single transform (class or object), or a tuple of transform objects, it fails in the setter:
Traceback (most recent call last):
File "galleries/examples/subplots_axes_and_figures/secondary_axis.py", line 40, in <module>
secax = ax.secondary_xaxis('top', functions=IdentityTransform)
File "lib/matplotlib/axes/_axes.py", line 586, in secondary_xaxis
secondary_ax = SecondaryAxis(self, 'x', location, functions,
File "lib/matplotlib/axes/_secondary_axes.py", line 42, in __init__
self.set_functions(functions)
File "lib/matplotlib/axes/_secondary_axes.py", line 155, in set_functions
raise ValueError('functions argument of secondary axes '
ValueError: functions argument of secondary axes must be a two-tuple of callable functions with the first function being the transform and the second being the inverseWith a tuple of transform classes, the setter allows it, but it fails when drawing:
Traceback (most recent call last):
File "lib/matplotlib/backends/backend_qt.py", line 461, in _draw_idle
self.draw()
File "lib/matplotlib/backends/backend_agg.py", line 401, in draw
self.figure.draw(self.renderer)
File "lib/matplotlib/artist.py", line 95, in draw_wrapper
result = draw(artist, renderer, *args, **kwargs)
File "lib/matplotlib/artist.py", line 72, in draw_wrapper
return draw(artist, renderer)
File "lib/matplotlib/figure.py", line 3115, in draw
artists = self._get_draw_artists(renderer)
File "lib/matplotlib/figure.py", line 225, in _get_draw_artists
child.apply_aspect(
File "lib/matplotlib/axes/_secondary_axes.py", line 120, in apply_aspect
self._set_lims()
File "lib/matplotlib/axes/_secondary_axes.py", line 216, in _set_lims
lims = self._functions[0](np.array(lims))
File "lib/matplotlib/transforms.py", line 1759, in __init__
super().__init__(*args, **kwargs)
File "lib/matplotlib/transforms.py", line 125, in __init__
self._shorthand_name = shorthand_name or ''
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
Expected outcome
At least one of the options works, or it should not be documented as accepted.
Additional information
I noticed this oddity in the types while reviewing #25224, but not sure what we intend here.
Operating system
No response
Matplotlib Version
Matplotlib Backend
No response
Python version
No response
Jupyter version
No response
Installation
git checkout
Activity
jklymak commented on Apr 15, 2023
That seems like an oversight, or something that got lost in the shuffle of adding a forward and inverse.
I don't think we should allow a tuple of transforms - one of the advantages of using a transform is that it has an inverse?
QuLogic commented on May 5, 2023
I don't think it's necessary; it's just something I tried to get past the checks and see if the internals were fine with it.