Grid lines configuration in Matplotlib - Mini Project: Build & Apply

Grid lines configuration

📖 Scenario: You are creating a simple line chart to show sales over a week. You want to make the chart easier to read by adding grid lines.

🎯 Goal: Build a line chart using matplotlib with grid lines enabled and customized.

📋 What You'll Learn

Create a list called days with the days of the week as strings.

Create a list called sales with sales numbers for each day.

Create a variable called grid_style to set the style of grid lines.

Plot the sales data using plt.plot().

Enable grid lines using plt.grid() with the style from grid_style.

Print the plot with grid lines visible.

💡 Why This Matters

🌍 Real World

Grid lines help people read charts more easily by showing reference lines behind the data points.

💼 Career

Data scientists and analysts often customize plots to make data clearer and more professional for reports and presentations.

1

Create sales data lists

Create a list called days with these exact values: 'Mon', 'Tue', 'Wed', 'Thu', 'Fri'. Create another list called sales with these exact values: 150, 200, 170, 220, 180.

Matplotlib

# Create the lists days and sales with the exact values
# Your code here

Hint

Use square brackets to create lists. Separate items with commas.

2

Set grid line style

Create a variable called grid_style and set it to the string '--' to represent dashed grid lines.

Matplotlib

days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri']
sales = [150, 200, 170, 220, 180]
# Create grid_style variable with value '--'
# Your code here

Hint

Assign the string '--' to the variable grid_style.

3

Plot sales and enable grid lines

Import matplotlib.pyplot as plt. Use plt.plot() with days and sales to create the line chart. Then enable grid lines using plt.grid() with the argument linestyle=grid_style.

Matplotlib

days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri']
sales = [150, 200, 170, 220, 180]
grid_style = '--'
# Import matplotlib.pyplot as plt
# Plot days vs sales
# Enable grid lines with linestyle=grid_style
# Your code here

Hint

Use import matplotlib.pyplot as plt to import. Use plt.plot() to plot. Use plt.grid(linestyle=grid_style) to add grid lines.

4

Display the plot

Use plt.show() to display the plot with the grid lines.

Matplotlib

import matplotlib.pyplot as plt

days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri']
sales = [150, 200, 170, 220, 180]
grid_style = '--'

plt.plot(days, sales)
plt.grid(linestyle=grid_style)
# Display the plot
# Your code here

Hint

Call plt.show() to open the plot window.

Practice

1. What does the plt.grid(True) command do in a matplotlib plot?

easy

A. It turns on the grid lines on the plot.

B. It hides the grid lines on the plot.

C. It changes the color of the grid lines to blue.

D. It saves the plot as an image file.

Solution

1. Step 1: Understand the plt.grid function

   The plt.grid() function controls the visibility of grid lines on the plot.

2. Step 2: Effect of passing True

   Passing True to plt.grid() turns the grid lines on, making them visible.

3. Final Answer:

   It turns on the grid lines on the plot. -> Option A

4. Quick Check:

   plt.grid(True) = grid visible [OK]

Hint: True means grid lines show, False hides them [OK]

Common Mistakes:

• Thinking plt.grid(True) hides grid lines
• Confusing grid color change with visibility
• Assuming plt.grid(True) saves the plot

2. Which of the following is the correct syntax to set grid lines only on the y-axis in matplotlib?

easy

A. plt.grid(axis='y')

B. plt.grid(axis='xy')

C. plt.grid(axis='x')

D. plt.grid(axis='z')

Solution

1. Step 1: Understand the axis parameter in plt.grid

   The axis parameter controls which axis the grid lines appear on: 'x', 'y', or 'both'.

2. Step 2: Correct value for y-axis grid lines

   To show grid lines only on the y-axis, use axis='y'. Other options like 'xy' or 'z' are invalid.

3. Final Answer:

   plt.grid(axis='y') -> Option A

4. Quick Check:

   axis='y' shows horizontal grid lines [OK]

Hint: Use axis='y' to show grid lines horizontally only [OK]

Common Mistakes:

• Using axis='xy' which is invalid
• Using axis='x' to get y-axis grid lines
• Using axis='z' which does not exist

3. What will be the effect of the following code snippet?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.grid(True, linestyle='--', color='red')
plt.show()

medium

A. Grid lines will be visible as solid black lines.

B. Code will raise a syntax error.

C. Grid lines will not be visible.

D. Grid lines will be visible as dashed red lines.

Solution

1. Step 1: Analyze plt.grid parameters

   The plt.grid() function is called with True to enable grid lines, linestyle='--' for dashed lines, and color='red' for red color.

2. Step 2: Understand the visual effect

   These parameters make the grid lines visible, dashed, and red in color on the plot.

3. Final Answer:

   Grid lines will be visible as dashed red lines. -> Option D

4. Quick Check:

   grid(True, linestyle='--', color='red') = dashed red grid [OK]

Hint: linestyle='--' and color='red' style grid lines [OK]

Common Mistakes:

• Assuming default solid black grid lines
• Thinking grid lines are hidden without plt.show()
• Expecting syntax error from valid parameters

4. Identify the error in this code that tries to show grid lines only on the x-axis:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.grid(axis='x', visible=true)
plt.show()

medium

A. plt.grid() cannot be used with plt.plot().

B. The axis='x' should be axis='y' to show x-axis grid lines.

C. true is undefined; use True (capitalized) instead.

D. Missing plt.show() to display the plot.

Solution

1. Step 1: Check plt.grid parameters

   The code raises NameError because true is not defined in Python. Boolean true is True (capitalized).

2. Step 2: Correct way to enable grid on x-axis

   Use plt.grid(True, axis='x') or plt.grid(visible=True, axis='x').

3. Final Answer:

   true is undefined; use True (capitalized) instead. -> Option C

4. Quick Check:

   plt.grid(True, axis='x') is correct [OK]

Hint: Booleans in Python are True/False (capitalized) [OK]

Common Mistakes:

• Using lowercase 'true' which causes NameError
• Confusing axis='x' with axis='y'
• Thinking plt.grid can't be used with plt.plot

5. You want to create a plot with grid lines only on the y-axis, styled as dotted blue lines, but only for major ticks. Which code snippet achieves this correctly?

hard

A. plt.grid(axis='y', linestyle=':', color='blue', which='minor')

B. plt.grid(True, axis='y', linestyle=':', color='blue', which='major')

C. plt.grid(True, axis='y', linestyle='--', color='blue', which='minor')

D. plt.grid(True, axis='x', linestyle=':', color='blue', which='major')

Solution

1. Step 1: Understand parameters for grid customization

   To show grid lines only on the y-axis, use axis='y'. For dotted lines, use linestyle=':'. To color them blue, use color='blue'. To apply only to major ticks, use which='major'.

2. Step 2: Verify each option

   plt.grid(True, axis='y', linestyle=':', color='blue', which='major') matches all requirements. plt.grid(axis='y', linestyle=':', color='blue', which='minor') uses which='minor', incorrect. plt.grid(True, axis='y', linestyle='--', color='blue', which='minor') uses minor ticks and dashed lines, incorrect. plt.grid(True, axis='x', linestyle=':', color='blue', which='major') applies to x-axis, not y-axis.

3. Final Answer:

   plt.grid(True, axis='y', linestyle=':', color='blue', which='major') -> Option B

4. Quick Check:

   axis='y', linestyle=':', color='blue', which='major' = plt.grid(True, axis='y', linestyle=':', color='blue', which='major') [OK]

Hint: Use which='major' and axis='y' for dotted blue y-grid [OK]

Common Mistakes:

• Using axis='x' instead of 'y'
• Forgetting which='major' to limit grid lines
• Missing True to enable grid lines