8000 Example for using cursor_data by timhoffm · Pull Request #12451 · matplotlib/matplotlib · GitHub
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Example for using cursor_data #12451

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1 change: 1 addition & 0 deletions .flake8
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Expand Up @@ -102,6 +102,7 @@ per-file-ignores =
examples/color/colormap_reference.py: E402
examples/color/custom_cmap.py: E402
examples/color/named_colors.py: E402
examples/event_handling/cursor_data.py: E402
examples/event_handling/data_browser.py: E501
examples/event_handling/path_editor.py: E501
examples/event_handling/pick_event_demo.py: E501
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55 changes: 55 additions & 0 deletions examples/event_handling/cursor_data.py
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"""
===========
Cursor Data
===========

This example demonstrates how to monkeypatch `.Artist.get_cursor_data` and
`.Artist.format_cursor_data` to show the elements under the cursor in the
status bar of the plot window.

.. image:: ../../_static/cursor_data.png

"""

import matplotlib.pyplot as plt
from matplotlib.lines import Line2D


def lines_under_cursor(self, event):
"""
Return a list of lines under the cursor for the given MouseMove event.
"""
if not event.inaxes:
return []
return [line for line in event.inaxes.lines if line.contains(event)[0]]


def format_lines(self, data):
"""Convert a list of lines to a comma-separted string."""
return ', '.join("Line('%s')" % line.get_label() for line in data)


Line2D.mouseover = True
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I'd rather you monkeypatch just the line instances that get returned by ax.plot; monkeypatching the classes themselves is a bit too global for me :)

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That would add the trouble of binding a method to an existing object. It makes it even more complicated to understand what's going on:

import matplotlib.pyplot as plt
import types


def patch_line(line):
    """Monkeypatch a line to show it's label on mouse-over."""

    def lines_under_cursor(self, event):
        """
        Return a list of lines under the cursor for the given MouseMove event.
        """
        if not event.inaxes:
            return []
        return [line for line in event.inaxes.lines if line.contains(event)[0]]

    def format_lines(self, data):
        """Convert a list of lines to a comma-separted string."""
        return ', '.join("Line('%s')" % line.get_label() for line in data)

    line.mouseover = True
    line.get_cursor_data = types.MethodType(lines_under_cursor, line)
    line.format_cursor_data = types.MethodType(format_lines, line)


fig, ax = plt.subplots()
l1, = ax.plot([1, 3, 2], label="Label 1", lw=3)
l2, = ax.plot([2, 1, 3], label="Label 2", lw=3)
patch_line(l1)
patch_line(l2)

plt.show()

Of course, you could bind a pure function in this case because self is not used, but that would lose generality.

Still not convinced that this monkey-patching is actually recommendable.

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Indeed, I would personally just bind free functions that don't take self as first argument. Doing it as suggested in your example is definitely overkill (as a side note, you can do line.get_cursor_data = get_cursor_data.__get__(type(line), line) which is a bit simpler IMO for the cases where you need it, or even just bind a partial() object... (there isn't much to gain by exactly binding a bound method)).

I'm not going to lose sleep over this specific example either way.

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Would it be more appropriate to subclass, such as:

class LabelShowingLine(Line2D):
    def get_cursor_data(self, event):
        ...

    def format_cursor_data(self, data):
        ...

ax.plot([1, 3, 2], label="Label 1", lw=3, cls=LabelShowingLine)

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l, = ax.plot(...)
l.__class__ = LabelShowingLine

hehe...

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FWIW this is how I would do it:

for line in ax.lines:
    line.lines_under_cursor = lambda event: (
        # Return a list of lines under the cursor for the given MouseEvent.
        [line for line in event.inaxes.lines if line.contains(event)[0]]
        if event.inaxes else [])
    line.format_lines = lambda data: (
        # Convert a list of lines into a comma-separated string.
        ", ".join("Line({!r})".format(line.get_label())) for line in data)

Line2D.get_cursor_data = lines_under_cursor
Line2D.format_cursor_data = format_lines

fig, ax = plt.subplots()
ax.plot([1, 3, 2], label="Label 1", lw=3)
ax.plot([2, 1, 3], label="Label 2", lw=3)

plt.show()


#############################################################################
#
# ------------
#
# References
# """"""""""
#
# The use of the following functions, methods, classes and modules is shown
# in this example:

import matplotlib
matplotlib.artist.Artist.get_cursor_data
matplotlib.artist.Artist.format_cursor_data
4 changes: 4 additions & 0 deletions lib/matplotlib/artist.py
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Expand Up @@ -1132,6 +1132,10 @@ def get_cursor_data(self, event):
The only current use case is displaying the z-value of an `.AxesImage`
in the status bar of a plot window, while moving the mouse.

Parameters
----------
event : `matplotlib.backend_bases.MouseEvent`

See Also
--------
format_cursor_data
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