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.

Practice

1. What is the main purpose of rcParams in matplotlib?

easy

A. To set global style defaults for all plots

B. To create new plots with random styles

C. To save plots as image files

D. To import data into matplotlib

Solution

1. Step 1: Understand what rcParams controls

   rcParams is a dictionary-like object in matplotlib that stores default settings for plot styles.

2. Step 2: Identify the purpose of setting rcParams

   Setting rcParams changes the default appearance of all plots globally, so you don't have to style each plot individually.

3. Final Answer:

   To set global style defaults for all plots -> Option A

4. Quick Check:

   rcParams = global style defaults [OK]

Hint: Remember rcParams sets defaults for all plots globally [OK]

Common Mistakes:

• Thinking rcParams creates plots
• Confusing rcParams with saving files
• Believing rcParams imports data

2. Which of the following is the correct way to change the default figure size using rcParams?

easy

A. plt.rcParams['figure.size'] = (8, 6)

B. plt.rcParams['figsize'] = (8, 6)

C. plt.rcParams['fig.size'] = (8, 6)

D. plt.rcParams['figure.figsize'] = (8, 6)

Solution

1. Step 1: Recall the exact rcParams key for figure size

   The correct key is 'figure.figsize', which expects a tuple for width and height.

2. Step 2: Check the syntax for assignment

   Assigning a tuple like (8, 6) to plt.rcParams['figure.figsize'] sets the default figure size.

3. Final Answer:

   plt.rcParams['figure.figsize'] = (8, 6) -> Option D

4. Quick Check:

   Key 'figure.figsize' = correct syntax [OK]

Hint: Use 'figure.figsize' key exactly for figure size [OK]

Common Mistakes:

• Using wrong key names like 'figsize' or 'figure.size'
• Assigning a list instead of a tuple
• Forgetting to import matplotlib.pyplot as plt

3. What will be the default line width for all plots after running this code?

import matplotlib.pyplot as plt
plt.rcParams['lines.linewidth'] = 3
print(plt.rcParams['lines.linewidth'])

medium

A. 1

B. 2

C. 3

D. Error

Solution

1. Step 1: Understand the code effect on rcParams

   The code sets 'lines.linewidth' to 3, changing the default line width globally.

2. Step 2: Check the printed value

   After setting, printing plt.rcParams['lines.linewidth'] outputs 3, confirming the change.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Set then print 'lines.linewidth' = 3 [OK]

Hint: Setting rcParams key changes default; print confirms value [OK]

Common Mistakes:

• Expecting default 1 without setting
• Confusing linewidth with linestyle
• Thinking print causes error

4. Identify the error in this code that tries to set the default font size:

import matplotlib.pyplot as plt
plt.rcParams['font.size'] = 'large'

medium

A. The key 'font.size' is incorrect

B. The value should be a number, not a string

C. plt.rcParams cannot be modified

D. Missing import statement

Solution

1. Step 1: Check the key correctness

   'font.size' is the correct rcParams key for font size.

2. Step 2: Validate the value type

   The value must be a number (int or float), not a string like 'large'.

3. Final Answer:

   The value should be a number, not a string -> Option B

4. Quick Check:

   font.size value must be numeric [OK]

Hint: Font size values must be numbers, not words [OK]

Common Mistakes:

• Using string values for numeric rcParams keys
• Assuming rcParams keys are case-insensitive
• Forgetting to import matplotlib.pyplot

5. You want all your matplotlib plots to have a dark background and white grid lines by default. Which rcParams settings should you apply?

hard

A. plt.rcParams['axes.facecolor'] = 'black'; plt.rcParams['grid.color'] = 'white'

B. plt.rcParams['figure.facecolor'] = 'white'; plt.rcParams['grid.color'] = 'black'

C. plt.rcParams['axes.facecolor'] = 'white'; plt.rcParams['grid.color'] = 'black'

D. plt.rcParams['figure.facecolor'] = 'black'; plt.rcParams['grid.color'] = 'black'

Solution

1. Step 1: Identify the rcParams key for plot background

   'axes.facecolor' sets the background color inside the plot area, so set it to 'black' for dark background.

2. Step 2: Identify the rcParams key for grid line color

   'grid.color' controls the color of grid lines; setting it to 'white' makes them visible on a dark background.

3. Final Answer:

   plt.rcParams['axes.facecolor'] = 'black'; plt.rcParams['grid.color'] = 'white' -> Option A

4. Quick Check:

   Dark background + white grid = axes.facecolor black, grid.color white [OK]

Hint: Use axes.facecolor for background, grid.color for grid lines [OK]

Common Mistakes:

• Changing figure.facecolor instead of axes.facecolor
• Setting grid color to black on black background
• Confusing axes and figure color keys