Rcparams for global defaults in Matplotlib - Step-by-Step Execution

Concept Flow - Rcparams for global defaults

Start Program

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Import matplotlib

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Set rcParams globally

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Plot graph

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Graph uses rcParams settings

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End Program

This flow shows how setting rcParams affects all plots globally in matplotlib.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
plt.rcParams['lines.linewidth'] = 3
plt.plot([1, 2, 3], [1, 4, 9])
plt.show()

This code sets the global line width to 3, then plots a simple line graph using that setting.

Execution Table

Step	Action	rcParams['lines.linewidth']	Plot Line Width	Output
1	Import matplotlib.pyplot as plt	default (1.5)	N/A	No plot yet
2	Set plt.rcParams['lines.linewidth'] = 3	3	N/A	No plot yet
3	Call plt.plot with data	3	3	Line plot prepared with width 3
4	Call plt.show()	3	3	Plot displayed with thick line width 3

💡 Plot displayed using updated global rcParams line width

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
rcParams['lines.linewidth']	1.5 (default)	3	3	3
Plot Line Width	N/A	N/A	3	3

Key Moments - 2 Insights

Why does changing rcParams affect all future plots?

Because rcParams is a global dictionary that matplotlib reads each time a plot is created, so changing it updates default styles for all plots after the change (see execution_table steps 2 and 3).

Does changing rcParams affect plots made before the change?

No, only plots created after the rcParams change use the new settings. Previous plots keep their original styles (see execution_table step 1 vs step 3).

Visual Quiz - 3 Questions

Look at the execution table, what is the line width used when plt.plot is called?

A 3

B 1.5

C default

D 0

💡 Hint

Check the 'Plot Line Width' column at Step 3 in the execution_table.

At which step does rcParams change from default to 3?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'rcParams["lines.linewidth"]' column in execution_table.

If we set rcParams['lines.linewidth'] = 5 instead of 3 at Step 2, what would be the plot line width at Step 3?

A 3

B 1.5

C 5

D default

💡 Hint

rcParams sets global defaults used by plots created after the change (see variable_tracker).

Concept Snapshot

matplotlib.rcParams is a global dictionary for default plot styles.
Change rcParams values to set global defaults (e.g., line width).
All plots created after the change use these new defaults.
Example: plt.rcParams['lines.linewidth'] = 3 sets thicker lines globally.
Use plt.show() to display plots with updated styles.

Full Transcript

This visual execution trace shows how matplotlib's rcParams dictionary controls global default styles for plots. First, matplotlib.pyplot is imported. Initially, the default line width is 1.5. When we set plt.rcParams['lines.linewidth'] = 3, this changes the global default line width to 3. Then, when we call plt.plot, the line uses the new width 3. Finally, plt.show() displays the plot with the thicker line. Changing rcParams affects all plots created after the change, but not those created before. This helps set consistent styles across multiple plots easily.