Mplcursors for hover labels in Matplotlib - Step-by-Step Execution

Concept Flow - Mplcursors for hover labels

Create plot with points

↓

Attach mplcursors to plot

↓

Hover over a point?

No→Wait

Yes↓

Show label with point info

↓

Move cursor away?

No→Keep label

Yes↓

Hide label

↓

End

The flow shows creating a plot, attaching mplcursors, then showing or hiding labels when hovering over points.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
import mplcursors

fig, ax = plt.subplots()
points = ax.scatter([1,2,3], [4,5,6])
cursor = mplcursors.cursor(points)
plt.show()

This code plots three points and attaches mplcursors to show labels when hovering.

Execution Table

Step	Action	Evaluation	Result
1	Create figure and axes	fig, ax = plt.subplots()	Figure and axes objects created
2	Plot points	ax.scatter([1,2,3], [4,5,6])	Scatter plot with 3 points created
3	Attach mplcursors	cursor = mplcursors.cursor(points)	Cursor object attached to points
4	Hover over point at (1,4)?	Yes	Label with coordinates (1, 4) shown
5	Move cursor away	Yes	Label hidden
6	Hover over point at (2,5)?	Yes	Label with coordinates (2, 5) shown
7	Move cursor away	Yes	Label hidden
8	Hover over point at (3,6)?	Yes	Label with coordinates (3, 6) shown
9	Move cursor away	Yes	Label hidden
10	No more hover	No	Wait for user action

💡 User stops hovering, program waits or ends

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	After Step 9
fig	None	Figure object	Figure object	Figure object	Figure object	Figure object	Figure object	Figure object	Figure object
ax	None	Axes object	Axes object	Axes object	Axes object	Axes object	Axes object	Axes object	Axes object
points	None	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points	Scatter object with 3 points
cursor	None	None	Cursor object attached	Cursor object attached	Cursor object attached	Cursor object attached	Cursor object attached	Cursor object attached	Cursor object attached
label_visible	False	False	False	True (point 1)	False	True (point 2)	False	True (point 3)	False

Key Moments - 2 Insights

Why does the label only appear when I hover exactly over a point?

The mplcursors cursor is attached to the scatter points, so it only triggers labels when the mouse is close enough to a point, as shown in steps 4, 6, and 8 in the execution_table.

What happens if I move the cursor away from the point?

The label disappears as shown in steps 5, 7, and 9 in the execution_table, because mplcursors hides the label when the cursor is no longer hovering over the point.

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What is the label_visible state?

A False

B True (point 1)

C True (point 2)

D None

💡 Hint

Check the variable_tracker row for label_visible at After Step 4.

At which step does the label for point (2,5) appear?

A Step 6

B Step 4

C Step 8

D Step 2

💡 Hint

Look at execution_table rows where label shows coordinates.

If you remove mplcursors.cursor(points), what changes in the execution?

A Labels still appear on hover

B Plot does not show points

C Labels never appear on hover

D Program crashes

💡 Hint

mplcursors.cursor attaches the hover label functionality as shown in step 3.

Concept Snapshot

Mplcursors adds interactive hover labels to matplotlib plots.
Use mplcursors.cursor(scatter) to attach.
Labels show when hovering near points.
Labels hide when cursor moves away.
No labels appear without mplcursors.

Full Transcript

This visual execution shows how mplcursors works with matplotlib scatter plots. First, a figure and axes are created. Then points are plotted with scatter. Next, mplcursors.cursor is attached to the points. When the user moves the mouse over a point, a label with the point's coordinates appears. Moving the mouse away hides the label. This repeats for each point hovered. Variables like fig, ax, points, cursor, and label visibility change step by step. Key moments clarify why labels only appear on hover and disappear when moving away. The quiz tests understanding of label visibility states and the role of mplcursors.