Text annotations in Matplotlib - Step-by-Step Execution

Concept Flow - Text annotations

Create plot data

↓

Plot data points

↓

Add annotation text

↓

Set annotation position

↓

Display plot with annotation

The flow shows creating data, plotting it, adding text annotations at specific points, and displaying the final plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
plt.plot(x, y, 'o')
plt.annotate('Point 2', (2, 5))
plt.show()

This code plots three points and adds a text annotation 'Point 2' at the coordinates (2, 5).

Execution Table

Step	Action	Data/Variables	Result/Output
1	Import matplotlib.pyplot as plt	plt module imported	Ready to plot
2	Define x and y data	x=[1,2,3], y=[4,5,6]	Data ready for plotting
3	Plot points with 'o' marker	x and y lists	Scatter plot with 3 points displayed
4	Add annotation text 'Point 2' at (2,5)	Annotation text and position	Text label appears near point (2,5)
5	Show plot	Plot with points and annotation	Plot window opens showing points and annotation
6	End	N/A	Plot displayed, execution complete

💡 Plot displayed with points and annotation; program ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
x	undefined	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]
y	undefined	[4, 5, 6]	[4, 5, 6]	[4, 5, 6]	[4, 5, 6]
plt	undefined	matplotlib.pyplot module	plot object created	annotation added	plot shown

Key Moments - 2 Insights

Why does the annotation text appear at (2, 5) and not at the data point (2, 5) exactly?

The annotation position is set at (2, 5) but matplotlib places the text slightly offset by default to avoid overlapping the marker, as seen in step 4 of the execution_table.

What happens if we add annotation before plotting points?

If annotation is added before plotting, the text may appear but without points plotted yet, so the visual context is missing. The execution_table shows plotting happens first (step 3) before annotation (step 4).

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the annotation text added?

A "Point 3"

B "Point 2"

C "Data Point"

D "Annotation"

💡 Hint

Check the 'Action' and 'Result/Output' columns at step 4 in execution_table.

At which step does the plot with points first appear?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Result/Output' column to find when points are plotted.

If we change annotation position to (3, 6), how does the variable 'plt' state change after step 4?

A No change in annotation position

B Annotation removed

C Annotation added at (3, 6)

D Plot points removed

💡 Hint

Refer to variable_tracker and execution_table step 4 about annotation position.

Concept Snapshot

Text annotations in matplotlib:
- Use plt.annotate(text, (x, y)) to add labels
- Place text near data points for clarity
- Plot data first, then annotate
- Annotation position is coordinate-based
- plt.show() displays the final plot

Full Transcript

This lesson shows how to add text annotations to a matplotlib plot. First, we import matplotlib.pyplot as plt. Then we create data lists x and y. Next, we plot these points using plt.plot with circle markers. After plotting, we add a text annotation using plt.annotate with the label 'Point 2' at coordinates (2, 5). Finally, plt.show() displays the plot with points and the annotation. The annotation text appears near the specified point but slightly offset to avoid overlap. The execution table traces each step, and the variable tracker shows how variables change. Key moments clarify common confusions about annotation placement and order of plotting. The visual quiz tests understanding of annotation text, plotting steps, and position changes. The snapshot summarizes how to use text annotations effectively in matplotlib.