Basic pie chart with plt.pie in Matplotlib - Step-by-Step Execution

Concept Flow - Basic pie chart with plt.pie

Prepare data values

↓

Call plt.pie() with data

↓

Matplotlib calculates slice sizes

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Draw pie slices on plot

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Display pie chart with plt.show()

This flow shows how data is prepared, passed to plt.pie(), which calculates and draws the pie slices, then displays the chart.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
sizes = [30, 20, 50]
plt.pie(sizes)
plt.show()

This code draws a pie chart with three slices sized 30, 20, and 50.

Execution Table

Step	Action	Input Data	Calculation	Output/Plot
1	Prepare data	[30, 20, 50]	Sum = 100	Data ready for pie chart
2	Call plt.pie()	[30, 20, 50]	Calculate slice angles: 108°, 72°, 180°	Slices sized accordingly
3	Draw slices	Angles from step 2	Draw arcs for each slice	Pie chart with 3 slices drawn
4	Show plot	Pie chart object	Render chart window	Pie chart displayed on screen
5	End	-	-	Execution complete

💡 All slices drawn and chart displayed, execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
sizes	undefined	[30, 20, 50]	[30, 20, 50]	[30, 20, 50]	[30, 20, 50]
sum_sizes	undefined	100	100	100	100
slice_angles	undefined	undefined	[108°, 72°, 180°]	[108°, 72°, 180°]	[108°, 72°, 180°]

Key Moments - 3 Insights

Why do the slice angles add up to 360 degrees?

Because plt.pie() converts data values into angles proportional to their share of the total sum, and a full circle is 360 degrees. See execution_table step 2.

What happens if the data values do not sum to 100?

plt.pie() automatically calculates the sum and scales slices accordingly, so the sum does not need to be 100. This is shown in variable_tracker where sum_sizes is calculated.

Why do we need plt.show() after plt.pie()?

plt.pie() prepares the pie chart but does not display it. plt.show() opens the window to display the chart. See execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the sum of the data values after step 1?

A 50

B 100

C 30

D 200

💡 Hint

Check the 'Calculation' column in execution_table row for step 1.

At which step are the pie slices actually drawn on the plot?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table to find when drawing happens.

If the sizes list changed to [10, 10, 80], how would the slice angles change?

A They would be [36°, 36°, 288°]

B They would be [30°, 20°, 50°]

C They would be [10°, 10°, 80°]

D They would be equal slices

💡 Hint

Use the formula: angle = (value / sum) * 360 degrees, see variable_tracker slice_angles.

Concept Snapshot

plt.pie(data)
- data: list of values for slices
- Automatically calculates slice sizes as % of total
- Draws pie chart slices
- Use plt.show() to display
- Slices angles sum to 360 degrees

Full Transcript

This visual execution shows how to create a basic pie chart using matplotlib's plt.pie function. First, data values are prepared as a list. Then plt.pie is called with this data, which calculates the sum and converts each value into an angle proportional to the total. The pie slices are drawn based on these angles. Finally, plt.show() displays the pie chart window. Variables like sizes, sum_sizes, and slice_angles track the data and calculations step-by-step. Key moments clarify why angles sum to 360 degrees, how plt.pie handles sums, and the role of plt.show(). The quizzes test understanding of sums, drawing steps, and angle calculations for different data.