Matplotlib for data visualization in Raspberry Pi - Step-by-Step Execution

Concept Flow - Matplotlib for data visualization

Import matplotlib.pyplot as plt

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Prepare data to plot

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Call plotting function (e.g., plt.plot)

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Customize plot (title, labels, legend)

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Display plot with plt.show()

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Plot appears

This flow shows how to create a plot step-by-step: import, prepare data, plot, customize, then display.

Execution Sample

Raspberry Pi

import matplotlib.pyplot as plt
x = [1, 2, 3, 4]
y = [10, 20, 25, 30]
plt.plot(x, y)
plt.title('Simple Line Plot')
plt.show()

This code draws a simple line plot of y versus x and shows it on screen.

Execution Table

Step	Action	Data/Variables	Plot State	Output
1	Import matplotlib.pyplot as plt	plt module ready	No plot yet	No output
2	Prepare data x and y	x=[1,2,3,4], y=[10,20,25,30]	No plot yet	No output
3	Call plt.plot(x, y)	x and y used	Line plot created with points (1,10),(2,20),(3,25),(4,30)	No output
4	Set title 'Simple Line Plot'	Title set	Plot has title	No output
5	Call plt.show()	Plot ready	Plot window opens	Line plot displayed on screen
6	End of script	All done	Plot shown	Script ends

💡 Plot displayed and script ends after plt.show()

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
plt	Not imported	Imported matplotlib.pyplot	Plot function ready	Plot title set	Plot displayed
x	Undefined	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]
y	Undefined	[10, 20, 25, 30]	[10, 20, 25, 30]	[10, 20, 25, 30]	[10, 20, 25, 30]

Key Moments - 3 Insights

Why do we need to call plt.show() at the end?

plt.show() tells Python to open the window and display the plot. Without it, the plot is created but not shown (see execution_table step 5).

What happens if x and y lists have different lengths?

Matplotlib will give an error because it needs matching points to plot. This is why x and y must be the same length (see variable_tracker for x and y).

Can we add a title before calling plt.plot()?

Yes, but usually we add the title after creating the plot so it applies to the current figure (see execution_table steps 3 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the plot state after step 3?

A Line plot created with points (1,10),(2,20),(3,25),(4,30)

B No plot created yet

C Plot window opened

D Title set but no plot

💡 Hint

Check the 'Plot State' column in row for step 3 in execution_table

At which step does the plot window open and display the graph?

A Step 2

B Step 5

C Step 3

D Step 6

💡 Hint

Look for 'Plot window opens' in the Output column of execution_table

If we forget to call plt.show(), what will happen?

A Plot will display automatically

B Python will crash

C Plot will be created but not shown

D Title will not appear

💡 Hint

Refer to key_moments about the role of plt.show() and execution_table step 5

Concept Snapshot

Matplotlib basics:
- Import with 'import matplotlib.pyplot as plt'
- Prepare data lists x and y
- Use plt.plot(x, y) to create line plot
- Customize with plt.title(), plt.xlabel(), plt.ylabel()
- Show plot with plt.show()
Always call plt.show() to see the plot window.

Full Transcript

This lesson shows how to create a simple line plot using Matplotlib. First, we import the pyplot module as plt. Then we prepare data lists x and y. Next, we call plt.plot(x, y) to create the line plot. We add a title with plt.title(). Finally, plt.show() displays the plot window. Variables x and y hold the data points. The plot is created but only appears after plt.show() is called. If x and y lengths differ, Matplotlib will error. Adding title usually happens after plotting. Remember, plt.show() is essential to see the plot.