Arrow annotations in Matplotlib - Step-by-Step Execution

Concept Flow - Arrow annotations

Create plot

↓

Define arrow start and end points

↓

Call annotation function with arrowprops

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Arrow drawn on plot

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Display plot with arrow annotation

The flow shows creating a plot, defining arrow points, calling annotation with arrow properties, drawing the arrow, and displaying the plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [1, 4, 9])
plt.annotate('Peak', xy=(2,4), xytext=(1.5,7), arrowprops=dict(facecolor='blue'))
plt.show()

This code plots points and adds an arrow annotation pointing to (2,4) labeled 'Peak'.

Execution Table

Step	Action	Input/Parameters	Effect/Output
1	Create plot line	Points: x=[1,2,3], y=[1,4,9]	Line plotted connecting points
2	Call annotate	text='Peak', xy=(2,4), xytext=(1.5,7), arrowprops={'facecolor':'blue'}	Arrow drawn from (1.5,7) to (2,4) with blue arrowhead and text 'Peak'
3	Display plot	plt.show()	Plot window opens showing line and arrow annotation

💡 Plot displayed with arrow annotation pointing to data point (2,4)

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	[1,2,3]	[1,2,3]	[1,2,3]	[1,2,3]
y	[1,4,9]	[1,4,9]	[1,4,9]	[1,4,9]
annotation_text	''	''	'Peak'	'Peak'
arrow_start	None	None	(1.5,7)	(1.5,7)
arrow_end	None	None	(2,4)	(2,4)
arrowprops	None	None	{'facecolor':'blue'}	{'facecolor':'blue'}

Key Moments - 3 Insights

Why does the arrow point from xytext to xy and not the other way?

The annotate function uses xytext as the arrow tail (text location) and xy as the arrow head (pointed location), as shown in execution_table step 2.

What happens if arrowprops is omitted?

Without arrowprops, no arrow is drawn; only the text appears at xytext, as the arrow drawing depends on arrowprops (see step 2).

Can the arrow color be changed?

Yes, by setting 'facecolor' or 'color' in arrowprops dictionary, like {'facecolor':'blue'} in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the arrow's end point (xy) at step 2?

A (1.5,7)

B (2,4)

C (3,9)

D (0,0)

💡 Hint

Check the 'Input/Parameters' column in step 2 for xy value.

At which step is the arrow actually drawn on the plot?

A Step 2

B Step 3

C Step 1

D No arrow is drawn

💡 Hint

Look at the 'Effect/Output' column describing arrow drawing.

If arrowprops is removed from annotate, what changes in the output?

A Plot line disappears

B Arrow is drawn with default style

C No arrow is drawn, only text appears

D Plot window does not open

💡 Hint

Refer to key_moments about arrowprops effect.

Concept Snapshot

matplotlib arrow annotations:
Use plt.annotate(text, xy, xytext, arrowprops) to add arrows.
xy is arrow tip location, xytext is text location.
arrowprops dict controls arrow style (color, shape).
Without arrowprops, no arrow is drawn.
Call plt.show() to display the plot.

Full Transcript

This visual execution traces how matplotlib draws arrow annotations. First, a plot line is created connecting points (1,1), (2,4), and (3,9). Then, plt.annotate is called with text 'Peak', arrow pointing from xytext (1.5,7) to xy (2,4), and arrowprops specifying a blue arrowhead. Finally, plt.show() displays the plot with the arrow annotation. Variables like x, y, annotation_text, arrow_start, arrow_end, and arrowprops are tracked through these steps. Key points include understanding that the arrow points from xytext to xy, arrowprops controls arrow appearance, and omitting arrowprops means no arrow is drawn. The quizzes test understanding of arrow endpoints, drawing step, and arrowprops effect. The snapshot summarizes usage and key rules for arrow annotations in matplotlib.