Legend placement and styling in Matplotlib - Step-by-Step Execution

Concept Flow - Legend placement and styling

Create plot with data

↓

Add legend with default placement

↓

Choose legend location

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Apply styling options

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Display plot with styled legend

The flow shows creating a plot, adding a legend, choosing where to place it, styling it, and then displaying the final plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1,2,3], label='Line 1')
plt.legend(loc='upper left', fontsize=10, shadow=True)
plt.show()

This code plots a line, adds a legend at the upper left with font size 10 and shadow, then shows the plot.

Execution Table

Step	Action	Legend Location	Font Size	Shadow	Result
1	Plot line with label	None	Default	False	Line plotted, no legend yet
2	Add legend with loc='upper left'	upper left	Default	False	Legend appears at upper left
3	Set fontsize=10	upper left	10	False	Legend font size changed
4	Enable shadow=True	upper left	10	True	Legend shadow enabled
5	Show plot	upper left	10	True	Plot displayed with styled legend

💡 Plot displayed with legend placed and styled as specified

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
legend_location	None	None	upper left	upper left	upper left	upper left
legend_fontsize	Default	Default	Default	10	10	10
legend_shadow	False	False	False	False	True	True

Key Moments - 3 Insights

Why does the legend not appear until plt.legend() is called?

The legend is created and shown only when plt.legend() is called, as shown in execution_table step 2 where the legend location changes from None to 'upper left'.

How does changing the 'loc' parameter affect the legend?

Changing 'loc' moves the legend to different positions on the plot, as seen in step 2 where 'upper left' places the legend in the top-left corner.

What effect does setting shadow=True have?

Setting shadow=True adds a shadow behind the legend box, making it visually distinct, as shown in step 4 where shadow changes from False to True.

Visual Quiz - 3 Questions

Look at the execution table, what is the legend location after step 3?

A None

B lower right

C upper left

D center

💡 Hint

Check the 'Legend Location' column in the execution_table at step 3

At which step does the legend shadow become enabled?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Shadow' column in the execution_table to see when it changes to True

If we remove the fontsize parameter, what would be the font size after step 3?

A Default

B 10

C Shadowed

D None

💡 Hint

Refer to the 'Font Size' column in execution_table and variable_tracker for default values

Concept Snapshot

matplotlib legend placement and styling:
- Use plt.legend(loc='position') to place legend (e.g., 'upper left')
- Customize font size with fontsize=number
- Add shadow with shadow=True
- Call plt.legend() after plotting data
- Show plot with plt.show()

Full Transcript

This visual execution traces how to place and style a legend in matplotlib. First, a line plot is created with a label. Then plt.legend() is called with location 'upper left' to place the legend. Next, the font size is set to 10, and shadow is enabled. Finally, the plot is displayed showing the styled legend. Variables like legend location, font size, and shadow state change step-by-step. Key moments clarify why the legend appears only after plt.legend(), how location affects placement, and what shadow does. Quiz questions test understanding of legend location, shadow enabling step, and default font size behavior.