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[Bug]: Validation not performed for loc argument to legend #24605

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#25281
Closed
[Bug]: Validation not performed for loc argument to legend#24605
#25281
Labels
Difficulty: Easyhttps://matplotlib.org/devdocs/devel/contribute.html#good-first-issuesGood first issueOpen a pull request against these issues if there are no active ones!
Milestone
v3.8.0
@iofall

Description

@iofall
iofall
opened on Dec 3, 2022

Bug summary

When passing non-str loc values to legend, validation is not performed. So even for invalid inputs, errors are raised only when we call show()

Code for reproduction

>>> import matplotlib.pyplot as plt
>>> import matplotlib as mpl
>>> xs, ys = [1,2,3], [2,3,1]
>>> fig, ax = plt.subplots(3)
>>> ax[0].scatter(xs, ys, label='loc-tuple-arg')
<matplotlib.collections.PathCollection object at 0x0000019D4099ED60>
>>> ax[0].legend(loc=(1.1, .5, 1.1, "abc"))
<matplotlib.legend.Legend object at 0x0000019D4099EF10>
>>> plt.show()

Actual outcome

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Me\anaconda3\envs\MPL\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\tkinter\__init__.py", line 814, in callit
    func(*args)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\_backend_tk.py", line 251, in idle_draw
    self.draw()
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 10, in draw
    super().draw()
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\backend_agg.py", line 405, in draw
    self.figure.draw(self.renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 74, in draw_wrapper
    result = draw(artist, renderer, *args, **kwargs)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\figure.py", line 3071, in draw
    mimage._draw_list_compositing_images(
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\image.py", line 131, in _draw_list_compositing_images
    a.draw(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\axes\_base.py", line 3107, in draw
    mimage._draw_list_compositing_images(
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\image.py", line 131, in _draw_list_compositing_images
    a.draw(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\legend.py", line 641, in draw
    bbox = self._legend_box.get_window_extent(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\offsetbox.py", line 354, in get_window_extent
    px, py = self.get_offset(w, h, xd, yd, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\offsetbox.py", line 291, in get_offset
    return (self._offset(width, height, xdescent, ydescent, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\legend.py", line 617, in _findoffset
    fx, fy = self._loc
ValueError: too many values to unpack (expected 2)
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Me\anaconda3\envs\MPL\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\tkinter\__init__.py", line 814, in callit
    func(*args)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\_backend_tk.py", line 251, in idle_draw
    self.draw()
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\backend_tkagg.py", line 10, in draw
    super().draw()
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\backends\backend_agg.py", line 405, in draw
    self.figure.draw(self.renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 74, in draw_wrapper
    result = draw(artist, renderer, *args, **kwargs)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\figure.py", line 3071, in draw
    mimage._draw_list_compositing_images(
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\image.py", line 131, in _draw_list_compositing_images
    a.draw(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\axes\_base.py", line 3107, in draw
    mimage._draw_list_compositing_images(
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\image.py", line 131, in _draw_list_compositing_images
    a.draw(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\artist.py", line 51, in draw_wrapper
    return draw(artist, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\legend.py", line 641, in draw
    bbox = self._legend_box.get_window_extent(renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\offsetbox.py", line 354, in get_window_extent
    px, py = self.get_offset(w, h, xd, yd, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\offsetbox.py", line 291, in get_offset
    return (self._offset(width, height, xdescent, ydescent, renderer)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\legend.py", line 617, in _findoffset
    fx, fy = self._loc
ValueError: too many values to unpack (expected 2)

Expected outcome

Errors should be raised when invalid arguments are passed to loc. Similar to what we get when we pass an invalid string value as shown:

>>> ax[0].legend(loc="abcd")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\axes\_axes.py", line 307, in legend
    self.legend_ = mlegend.Legend(self, handles, labels, **kwargs)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\_api\deprecation.py", line 454, in wrapper
    return func(*args, **kwargs)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\legend.py", line 470, in __init__
    loc = _api.check_getitem(self.codes, loc=loc)
  File "C:\Users\Me\anaconda3\envs\MPL\lib\site-packages\matplotlib\_api\__init__.py", line 190, in check_getitem
    raise ValueError(
ValueError: 'abcd' is not a valid value for loc; supported values are 'best', 'upper right', 'upper left', 'lower left', 'lower right', 'right', 'center left', 'center right', 'lower center', 'upper center', 'center'

Additional information

  • Do you know why this bug is happening?

    matplotlib/lib/matplotlib/legend.py

    Lines 608 to 615 in ab7917a

    def _set_loc(self, loc):
    # find_offset function will be provided to _legend_box and
    # _legend_box will draw itself at the location of the return
    # value of the find_offset.
    self._loc_used_default = False
    self._loc_real = loc
    self.stale = True
    self._legend_box.set_offset(self._findoffset)

No validation is done when setting values for _loc_real. We do check strings on line 473, which is why we don't face this issue there.

Operating system

Windows

Matplotlib Version

3.6.2

Matplotlib Backend

'TkAgg'

Python version

3.9.7

Jupyter version

No response

Installation

pip

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