Line styles (solid, dashed, dotted) in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What line style is used in this plot code?

Look at the code below that draws a line using matplotlib. What line style will the line have?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1, 2], [0, 1, 0], linestyle='--')
plt.show()

A Dashed line

B Solid line

C Dotted line

D Dash-dot line

💡 Hint

The linestyle argument controls the pattern of the line.

The linestyle='--' means the line will be dashed. Solid is '-', dotted is ':', and dash-dot is '-.'.

❓ data_output

intermediate

How many lines are solid in this plot code?

The code below plots three lines with different line styles. How many lines will be solid?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [1, 2, 3], linestyle='-')
plt.plot([1, 2, 3], [3, 2, 1], linestyle=':')
plt.plot([1, 2, 3], [2, 2, 2], linestyle='--')
plt.show()

A 1

B 0

C 2

D 3

💡 Hint

Check the linestyle argument for each plot call.

Only the first plot uses linestyle='-', which is solid. The others are dotted ':' and dashed '--'.

❓ visualization

advanced

Identify the line style of the green line in this plot

This code plots three lines with colors and line styles. What is the line style of the green line?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1, 2], [2, 1, 0], color='red', linestyle=':')
plt.plot([0, 1, 2], [0, 1, 2], color='green', linestyle='-.')
plt.plot([0, 1, 2], [1, 1, 1], color='blue', linestyle='--')
plt.show()

A Dashed line

B Dash-dot line

C Solid line

D Dotted line

💡 Hint

Look at the linestyle argument for the green line.

The green line uses linestyle='-.', which is dash-dot style.

🧠 Conceptual

advanced

What error occurs with this invalid linestyle?

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1], [1, 0], linestyle='---')
plt.show()

A No error, plots a solid line

B SyntaxError: invalid syntax

C TypeError: linestyle must be a string

D ValueError: Unrecognized linestyle string

💡 Hint

Check if '---' is a valid linestyle in matplotlib.

Matplotlib does not recognize '---' as a valid linestyle and raises a ValueError.

🔧 Debug

expert

Why does this plot not show a dotted line?

The code below is intended to plot a dotted line but does not. Why?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1, 2], [0, 1, 0], linestyle='..')
plt.show()

A Because the plot function requires linewidth to show dotted lines

B Because '..' is interpreted as two dots, producing a dotted line

C Because '..' is not a valid linestyle, matplotlib defaults to solid line

D Because linestyle must be a tuple, not a string

💡 Hint

Check the valid linestyle strings in matplotlib.

Matplotlib does not recognize '..' as a valid linestyle, so it falls back to solid line.

Practice

1. Which linestyle value in matplotlib creates a solid line?

easy

A. "-"

B. "--"

C. ":"

D. "-."

Solution

1. Step 1: Understand line style symbols in matplotlib

   In matplotlib, the linestyle parameter uses symbols: "-" for solid, "--" for dashed, ":" for dotted, and "-." for dash-dot.

2. Step 2: Match symbol to solid line

   The symbol "-" represents a solid line style.

3. Final Answer:

   "-" -> Option A

4. Quick Check:

   Solid line = "-" [OK]

Hint: Solid line uses a single dash "-" [OK]

Common Mistakes:

• Confusing dashed "--" with solid
• Using ":" for solid line
• Mixing dash-dot "-." with solid

2. Which of the following is the correct syntax to plot a dashed line using matplotlib.pyplot?

easy

A. plt.plot(x, y, linestyle='-')

B. plt.plot(x, y, linestyle=':')

C. plt.plot(x, y, linestyle='--')

D. plt.plot(x, y, linestyle='solid')

Solution

1. Step 1: Recall linestyle values for dashed lines

   Dashed lines in matplotlib are specified by the string "--" or the word "dashed".

2. Step 2: Identify correct syntax

   Among the options, only linestyle='--' correctly sets a dashed line.

3. Final Answer:

   plt.plot(x, y, linestyle='--') -> Option C

4. Quick Check:

   Dashed line = "--" [OK]

Hint: Dashed line uses double dash "--" [OK]

Common Mistakes:

• Using single dash '-' for dashed line
• Using ':' which is dotted line
• Using 'solid' string incorrectly

3. What will be the line style of the plot generated by this code?

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [2, 3, 5]
plt.plot(x, y, linestyle=':')
plt.show()

medium

A. Dotted line

B. Dashed line

C. Solid line

D. Dash-dot line

Solution

1. Step 1: Identify linestyle parameter value

   The code uses linestyle=':', which in matplotlib means a dotted line.

2. Step 2: Understand line style mapping

   "-" is solid, "--" is dashed, ":" is dotted, and "-." is dash-dot.

3. Final Answer:

   Dotted line -> Option A

4. Quick Check:

   Colon ":" means dotted line [OK]

Hint: Colon ":" means dotted line style [OK]

Common Mistakes:

• Thinking ':' is dashed line
• Confusing dash-dot '-.' with dotted
• Assuming default solid line

4. The following code is intended to plot a dashed line but does not work as expected. What is the error?

import matplotlib.pyplot as plt
x = [0, 1, 2]
y = [0, 1, 4]
plt.plot(x, y, linestyle='dash')
plt.show()

medium

A. The list y has wrong values

B. The linestyle value 'dash' is invalid; use '--' instead

C. Missing plt.show() call

D. The variable names x and y are incorrect

Solution

1. Step 1: Check valid linestyle values in matplotlib

   Matplotlib accepts 'solid', 'dashed', 'dashdot', 'dotted' as strings or symbols like '--', '-.', ':'. The string 'dash' is invalid.

2. Step 2: Identify the error

   The code uses linestyle='dash', which is not a valid linestyle value. Use '--' for dashed lines.

3. Final Answer:

   The linestyle value 'dash' is invalid; use '--' instead -> Option B

4. Quick Check:

   Invalid 'dash'; use '--' [OK]

Hint: 'dash' invalid for dashed; use '--' [OK]

Common Mistakes:

• Assuming 'dash' string works
• Thinking plt.show() is missing
• Blaming variable names or data values

5. You want to plot two lines on the same graph: the first one solid and the second one dotted. Which code correctly sets these line styles?

hard

A. plt.plot(x, y1, linestyle='-.')
plt.plot(x, y2, linestyle=':')

B. plt.plot(x, y1, linestyle=':')
plt.plot(x, y2, linestyle='-')

C. plt.plot(x, y1, linestyle='-')
plt.plot(x, y2, linestyle='--')

D. plt.plot(x, y1, linestyle='-')
plt.plot(x, y2, linestyle=':')

Solution

1. Step 1: Identify line styles for solid and dotted

   Solid line uses "-" and dotted line uses ":" in matplotlib.

2. Step 2: Match code to required styles

   plt.plot(x, y1, linestyle='-') plt.plot(x, y2, linestyle=':') uses linestyle='-' for the first line (solid) and linestyle=':' for the second line (dotted), which is correct.

3. Final Answer:

   plt.plot(x, y1, linestyle='-') and plt.plot(x, y2, linestyle=':') -> Option D

4. Quick Check:

   Solid = '-', Dotted = ':' [OK]

Hint: Solid '-' and dotted ':' line styles together [OK]

Common Mistakes:

• Mixing dashed '--' with dotted ':'
• Using dash-dot '-.' instead of dotted
• Swapping line styles order