Line colors and width in Matplotlib - Step-by-Step Execution

Concept Flow - Line colors and width

Start Plot Setup

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Define x and y data

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Set line color and width

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Call plt.plot() with color and linewidth

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Render plot with plt.show()

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End

The flow shows setting up data, choosing line color and width, plotting, and displaying the plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3, 4]
y = [10, 20, 25, 30]
plt.plot(x, y, color='red', linewidth=3)
plt.show()

This code plots a red line with width 3 connecting points defined by x and y.

Execution Table

Step	Action	Parameter Set	Effect on Plot	Output
1	Import matplotlib.pyplot	-	Ready to plot	No visible output
2	Define x data	x = [1, 2, 3, 4]	Data points set	No visible output
3	Define y data	y = [10, 20, 25, 30]	Data points set	No visible output
4	Call plt.plot()	color='red', linewidth=3	Line color set to red, width set to 3	Line plotted on graph
5	Call plt.show()	-	Plot displayed	Graph window opens showing red thick line

💡 Plot displayed and program waits for user to close window

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
x	undefined	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]
y	undefined	undefined	[10, 20, 25, 30]	[10, 20, 25, 30]	[10, 20, 25, 30]
color	default (blue)	default (blue)	default (blue)	red	red
linewidth	default (1.5)	default (1.5)	default (1.5)	3	3

Key Moments - 3 Insights

Why does the line appear thicker when we set linewidth=3?

Because linewidth controls how thick the line is drawn. In the execution_table step 4, linewidth=3 makes the line wider than the default 1.5.

What happens if we do not specify the color parameter?

The line uses the default color (usually blue). This is shown in variable_tracker where color starts as default and changes only when set explicitly in step 4.

Can we use color names other than 'red'?

Yes, matplotlib accepts many color names or codes. The key moment is in step 4 where color='red' is set; changing 'red' to another valid color name changes the line color.

Visual Quiz - 3 Questions

Look at the variable_tracker table. What is the value of 'linewidth' after step 4?

A 3

B 1.5

C default

D undefined

💡 Hint

Check the 'linewidth' row under 'After Step 4' column in variable_tracker.

According to the execution_table, what action causes the line color to change to red?

A Defining y data

B Calling plt.plot() with color='red'

C Calling plt.show()

D Importing matplotlib.pyplot

💡 Hint

Look at step 4 in execution_table where color='red' is set.

If we remove the linewidth parameter from plt.plot(), what will happen to the line width?

A Line width becomes 3

B Line disappears

C Line width becomes default (1.5)

D Error occurs

💡 Hint

Refer to variable_tracker where linewidth starts as default and changes only when set.

Concept Snapshot

plt.plot(x, y, color='colorname', linewidth=number)
- color sets the line color (e.g., 'red', 'blue')
- linewidth sets thickness (default ~1.5)
- plt.show() displays the plot
- Omitting color or linewidth uses defaults
- Use simple color names or hex codes

Full Transcript

This lesson shows how to set line colors and widths in matplotlib plots. We start by importing matplotlib.pyplot, then define x and y data points. Next, we call plt.plot() with parameters color='red' and linewidth=3 to draw a red thick line connecting the points. Finally, plt.show() displays the plot window. The execution table traces each step, showing when variables like color and linewidth change. The variable tracker confirms how these parameters update after each step. Key moments clarify why linewidth affects thickness and how default colors apply if not set. The quiz tests understanding of these changes by referencing the tables. The snapshot summarizes the syntax and behavior for quick recall.