Rcparams for global defaults in Matplotlib - Mini Project: Build & Apply

Setting Global Plot Styles with RcParams in Matplotlib

📖 Scenario: You are preparing multiple charts for a presentation. You want all your plots to have the same style, like font size and line width, so they look consistent without changing each plot separately.

🎯 Goal: Learn how to set global default styles for all plots using matplotlib.rcParams. You will create a simple plot and change the global font size and line width so every plot uses these settings automatically.

📋 What You'll Learn

Create a dictionary with some sample data for plotting

Set global style defaults using matplotlib.rcParams

Plot the data using the default styles

Print the current global font size and line width settings

💡 Why This Matters

🌍 Real World

Setting global plot styles helps keep all charts in reports or presentations consistent and saves time by avoiding repeated style settings.

💼 Career

Data scientists and analysts often customize plot styles globally to maintain brand colors and readability in dashboards and reports.

1

Create sample data for plotting

Create a dictionary called data with keys 'x' and 'y'. Set 'x' to the list [1, 2, 3, 4, 5] and 'y' to the list [2, 3, 5, 7, 11].

Matplotlib

# Create a dictionary called data with keys 'x' and 'y'
data = {}
# Your code here

Hint

Use a dictionary with keys 'x' and 'y' and assign the exact lists as values.

2

Set global font size and line width using rcParams

Import matplotlib.pyplot as plt. Then set the global font size to 14 and the global line width to 3 using plt.rcParams.

Matplotlib

data = {'x': [1, 2, 3, 4, 5], 'y': [2, 3, 5, 7, 11]}
# Import matplotlib.pyplot as plt
# Set plt.rcParams['font.size'] to 14
# Set plt.rcParams['lines.linewidth'] to 3
# Your code here

Hint

Use plt.rcParams['font.size'] = 14 and plt.rcParams['lines.linewidth'] = 3 to set global styles.

3

Plot the data using the global defaults

Use plt.plot() to plot data['x'] and data['y']. Then call plt.show() to display the plot.

Matplotlib

import matplotlib.pyplot as plt

data = {'x': [1, 2, 3, 4, 5], 'y': [2, 3, 5, 7, 11]}

plt.rcParams['font.size'] = 14
plt.rcParams['lines.linewidth'] = 3

# Plot data['x'] vs data['y']
# Show the plot
# Your code here

Hint

Use plt.plot(data['x'], data['y']) and then plt.show() to display the plot.

4

Print the current global font size and line width

Print the values of plt.rcParams['font.size'] and plt.rcParams['lines.linewidth'] on separate lines.

Matplotlib

import matplotlib.pyplot as plt

data = {'x': [1, 2, 3, 4, 5], 'y': [2, 3, 5, 7, 11]}

plt.rcParams['font.size'] = 14
plt.rcParams['lines.linewidth'] = 3

plt.plot(data['x'], data['y'])
plt.show()

# Print the font size and line width
# Your code here

Hint

Use print(plt.rcParams['font.size']) and print(plt.rcParams['lines.linewidth']) to show the current settings.

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