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[Bug]: set linestyle='dashed' raise error with quiver and legend · Issue #28298 · matplotlib/matplotlib · GitHub

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[Bug]: set linestyle='dashed' raise error with quiver and legend #28298

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Closed
[Bug]: set linestyle='dashed' raise error with quiver and legend#28298
Labels
status: confirmed bugtopic: plotting methods
Milestone
v3.11.0

Description

quzhijing
opened on May 25, 2024

Bug summary

Issue description:
I am trying to print the linear arrow with dashed style, but there is error waring
"ValueError: At least one value in the dash list must be positive"

Code:
Part Code like following
plt.quiver(0, 0, v1[0], v1[1], angles='xy', scale_units='xy', scale=1, color='r', label='v1 (3, 4)', linestyle='solid')
plt.quiver(0, 0, v2[0], v2[1], angles='xy', scale_units='xy', scale=1, color='b', label='v2 (4, -3)', linestyle='solid')
v_sum = v1 + v2
plt.quiver(0, 0, v_sum[0], v_sum[1], angles='xy', scale_units='xy', scale=1, color='g', linestyle='dashed', linewidth=0, label='v1 + v2')

#I searched similar issue ticket: #8821 to set lw=0, it's still not work

enviroment:
my python version: Python 3.12.3
matplotlib version: 3.9.0

Code for reproduction

plt.quiver(0, 0, v1[0], v1[1], angles='xy', scale_units='xy', scale=1, color='r', label='v1 (3, 4)', linestyle='solid')
plt.quiver(0, 0, v2[0], v2[1], angles='xy', scale_units='xy', scale=1, color='b', label='v2 (4, -3)', linestyle='solid')
v_sum = v1 + v2
plt.quiver(0, 0, v_sum[0], v_sum[1], angles='xy', scale_units='xy', scale=1, color='g', linestyle='dashed', linewidth=0, label='v1 + v2')

Actual outcome

There is empty present

(mathenv) C:\WorkSpace\math>c:/WorkSpace/math/mathenv/Scripts/python.exe c:/WorkSpace/math/linearAnalog.py
Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Python312\Lib\tkinter_init_.py", line 1967, in call
return self.func(*args)
^^^^^^^^^^^^^^^^
File "C:\Python312\Lib\tkinter_init_.py", line 861, in callit
func(*args)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\backends_backend_tk.py", line 271, in idle_draw
self.draw()
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\backends\backend_tkagg.py", line 10, in draw
super().draw()
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\backends\backend_agg.py", line 387, in draw
self.figure.draw(self.renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 95, in draw_wrapper
result = draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 72, in draw_wrapper
return draw(artist, renderer)
^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\figure.py", line 3155, in draw
mimage._draw_list_compositing_images(
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\image.py", line 132, in _draw_list_compositing_images
a.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 72, in draw_wrapper
return draw(artist, renderer)
^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\axes_base.py", line 3109, in draw
mimage._draw_list_compositing_images(
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\image.py", line 132, in _draw_list_compositing_images
a.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 72, in draw_wrapper
return draw(artist, renderer)
^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\legend.py", line 777, in draw
self._legend_box.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 39, in draw_wrapper
return draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\offsetbox.py", line 383, in draw
c.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 39, in draw_wrapper
return draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\offsetbox.py", line 383, in draw
c.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 39, in draw_wrapper
return draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\offsetbox.py", line 383, in draw
c.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 39, in draw_wrapper
return draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\offsetbox.py", line 383, in draw
c.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 39, in draw_wrapper
return draw(artist, renderer, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\offsetbox.py", line 669, in draw
c.draw(renderer)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\artist.py", line 72, in draw_wrapper
return draw(artist, renderer)
^^^^^^^^^^^^^^^^^^^^^^
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\patches.py", line 632, in draw
self._draw_paths_with_artist_properties(
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\patches.py", line 594, in _draw_paths_with_artist_properties
gc.set_dashes(*self._dash_pattern)
File "c:\WorkSpace\math\mathenv\Lib\site-packages\matplotlib\backend_bases.py", line 924, in set_dashes
raise ValueError(
ValueError: At least one value in the dash list must be positive

Expected outcome

Expect the plt.quiver can print a dash arrow for the sum of two linear array

Additional information

No response

Operating system

No response

Matplotlib Version

3.9.0

Matplotlib Backend

No response

Python version

No response

Jupyter version

No response

Installation

None

Activity

  1. rcomer commented on May 26, 2024

    rcomer
    on May 26, 2024
    Member

    Hello @quzhijing thanks for the report. Please could you provide a complete code example that we can run to reproduce the problem?

  2. rcomer
    added
    status: needs clarificationIssues that need more information to resolve.
    topic: plotting methods
    on May 26, 2024

  3. quzhijing commented on May 30, 2024

    quzhijing
    on May 30, 2024
    Author

    @rcomer my complete code:

    import matplotlib.pyplot as plt
import numpy as np

# Set the plotting range
plt.figure(figsize=(10, 10))
plt.xlim(-10, 10)
plt.ylim(-10, 10)
plt.axhline(0, color='black', linewidth=0.5)
plt.axvline(0, color='black', linewidth=0.5)
plt.grid(color='gray', linestyle='--', linewidth=0.5)

# Define vectors
v1 = np.array([3, 4])
v2 = np.array([4, -3])

# Plot vectors v1 and v2
plt.quiver(0, 0, v1[0], v1[1], angles='xy', scale_units='xy', scale=1, color='r', label='v1 (3, 4)')
plt.quiver(0, 0, v2[0], v2[1], angles='xy', scale_units='xy', scale=1, color='b', label='v2 (4, -3)')

# Plot the sum of the vectors
v_sum = v1 + v2
line1 = plt.quiver(0, 0, v_sum[0], v_sum[1], angles='xy', scale_units='xy', scale=1, color='g', label='v1 + v2')
line1.set_linestyle('dashed')

# Plot the difference of the vectors
v_diff = v1 - v2
plt.quiver(0, 0, v_diff[0], v_diff[1], angles='xy', scale_units='xy', scale=1, color='y', linestyle='dashed',  facecolor='none', linewidth=1, label='v1 - v2')

# Plot scalar multiplication
scalar = 2
v_scalar = scalar * v1
plt.quiver(0, 0, v_scalar[0], v_scalar[1], angles='xy', scale_units='xy', scale=1, color='m', linestyle='dashed',  facecolor='none', linewidth=1, label='2 * v1')

# Plot vector dot product (projection explanation)
v2_unit = v2 / np.linalg.norm(v2)
projection_length = np.dot(v1, v2_unit)
projection = projection_length * v2_unit
plt.quiver(0, 0, projection[0], projection[1], angles='xy', scale_units='xy', scale=1, color='c', linestyle='dashed',  facecolor='none', linewidth=1, label='proj_v2(v1)')

# Add legend
plt.legend()

# Display the plot
plt.title('Basic Vector Operations in Linear Algebra')
plt.show()

  4. tacaswell commented on May 30, 2024

    tacaswell
    on May 30, 2024
    Member

    A minimal reproducer:

    plt.figure(figsize=(10, 10))
line1 = plt.quiver(0, 0, 7, 1, angles='xy', scale_units='xy', scale=1, color='g', label='v1 + v2', lw=0)
line1.set_linestyle('dashed')
plt.legend()
fig = plt.gcf()
plt.show()

    setting lw to be >0 or not showing the legend fixes the problem. Something is going wrong in generating the legend entry, I think because it is grabbing a post-scaled version of the dash pattern.

  5. tacaswell
    added this to the v3.9.1 milestone on May 30, 2024
  6. tacaswell
    added
    status: confirmed bug
    and removed
    status: needs clarificationIssues that need more information to resolve.
    on May 30, 2024

  7. quzhijing commented on May 31, 2024

    quzhijing
    on May 31, 2024
    Author

    @tacaswell Thanks, it's fixed after remote legend() show, So would we can expect to fix in newer version?

  8. tacaswell
    changed the title [-][Bug]: set linestyle='dashed' raise error[/-] [+][Bug]: set linestyle='dashed' raise error with quiver and legend[/+] on Jun 5, 2024

  9. QuLogic commented on Jun 28, 2024

    QuLogic
    on Jun 28, 2024
    Member

    quiver produces a Quiver, which is a PolyCollection, so the legend handler for that copies the linestyle as:

    matplotlib/lib/matplotlib/legend_handler.py

    Line 801 in 74c7f9a

    legend_handle.set_linestyle(get_first(orig_handle.get_linestyles()))

    The semantics between the setter and getter are a bit confused, so this is somewhat related to #23056, though unfortunately, that PR does not fix this bug.

  10. QuLogic
    modified the milestones: v3.9.1, v3.9.2 on Jul 4, 2024
  11. QuLogic
    modified the milestones: v3.9.2, v3.9.3 on Aug 12, 2024

  12. 5 remaining items

  13. ksunden
    modified the milestones: v3.10.2, v3.10.3 on May 2, 2025
  14. ksunden
    modified the milestones: v3.10.4, v3.10.5 on Jul 25, 2025
  15. ksunden
    modified the milestones: v3.10.6, v3.10.7 on Aug 29, 2025

  16. QuLogic commented on Sep 10, 2025

    QuLogic
    on Sep 10, 2025 · Hidden as outdated
  17. ksunden
    modified the milestones: v3.10.7, v3.10.8 on Oct 8, 2025
  18. ksunden
    modified the milestones: v3.10.8, v3.10.9 on Nov 13, 2025

  19. QuLogic commented on Mar 20, 2026

    QuLogic
    on Mar 20, 2026
    Member

    Fixed by #31307.

  20. QuLogic
    closed this as completedon Mar 20, 2026
  21. QuLogic
    modified the milestones: v3.10.9, v3.11.0 on Mar 20, 2026
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