Line colors and width in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the color of the line in this plot?

Look at the code below that plots a line. What color will the line be?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6], color='green')
plt.show()

A Blue

B Red

C Green

D Black

💡 Hint

The color is set by the 'color' parameter in plt.plot.

The line color is set to 'green' explicitly by the color='green' argument.

❓ Predict Output

intermediate

What is the width of the line plotted?

Check the code below. What is the width of the line shown in the plot?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1, 2], [2, 3, 4], linewidth=5)
plt.show()

A 5

B 10

C 0.5

D 1 (default width)

💡 Hint

The linewidth parameter controls the thickness of the line.

The linewidth is set to 5 by the linewidth=5 argument.

🔧 Debug

advanced

Why does this code raise an error?

This code tries to plot a red line with width 3 but raises an error. What is the cause?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [3, 2, 1], color='red', linewidth=3)
plt.show()

A linewidth should be line_width, so it's an invalid argument.

B The color value red is not in quotes, causing a NameError.

C plt.plot does not accept color or linewidth arguments.

D The lists for x and y have different lengths.

💡 Hint

String values must be in quotes in Python.

The color argument value red is not quoted, so Python treats it as a variable which is not defined.

❓ data_output

advanced

What is the RGB color code for the line?

The code below plots a line with color='cyan'. What is the RGB tuple for this color?

Matplotlib

import matplotlib.pyplot as plt
line = plt.plot([0, 1], [1, 0], color='cyan')
plt.show()

A (0.0, 1.0, 1.0)

B (1.0, 0.0, 0.0)

C (0.0, 0.0, 1.0)

D (1.0, 1.0, 0.0)

💡 Hint

Cyan is a mix of green and blue at full intensity.

In RGB, cyan is (0, 1, 1) meaning no red, full green, full blue.

🚀 Application

expert

How to plot two lines with different colors and widths?

You want to plot two lines on the same graph: one red line with width 2, and one blue line with width 4. Which code does this correctly?

A

import matplotlib.pyplot as plt
plt.plot([1,2,3], [3,2,1], color='red', linewidth=2)
plt.plot([1,2,3], [1,2,3], color='blue', linewidth=4)
plt.show()

B

import matplotlib.pyplot as plt
plt.plot([1,2,3], [3,2,1], 'red', 2)
plt.plot([1,2,3], [1,2,3], 'blue', 4)
plt.show()

C

import matplotlib.pyplot as plt
plt.plot([1,2,3], [3,2,1], color='red', width=2)
plt.plot([1,2,3], [1,2,3], color='blue', width=4)
plt.show()

D

import matplotlib.pyplot as plt
plt.plot([1,2,3], [3,2,1], c='red', linewidth=2)
plt.plot([1,2,3], [1,2,3], c='blue', linewidth=4)
plt.show()

💡 Hint

Use color= and linewidth= parameters correctly.

Options A and D use correct parameter names and values ('color' or its alias 'c'). Option B passes positional arguments incorrectly. Option C uses 'width' which is invalid.

Practice

1. Which parameter in matplotlib.pyplot.plot() changes the color of the line?

easy

A. linestyle

B. color

C. linewidth

D. marker

Solution

1. Step 1: Understand the purpose of parameters in plot()

   The color parameter sets the line color, while linewidth changes thickness.

2. Step 2: Identify the parameter for color

   Among the options, only color directly changes the line color.

3. Final Answer:

   color -> Option B

4. Quick Check:

   Line color = color [OK]

Hint: Remember: color changes color, linewidth changes thickness [OK]

Common Mistakes:

• Confusing linewidth with color
• Using linestyle to change color
• Trying to use marker for color

2. Which of the following is the correct syntax to set a red line with thickness 3 in matplotlib.pyplot.plot()?

easy

A. plt.plot(x, y, color='red', linewidth=3)

B. plt.plot(x, y, linewidth='red', color=3)

C. plt.plot(x, y, color=3, linewidth='red')

D. plt.plot(x, y, width=3, color='red')

Solution

1. Step 1: Check parameter names and values

   The correct parameters are color with a color string and linewidth with a number.

2. Step 2: Validate plt.plot(x, y, color='red', linewidth=3) syntax

   plt.plot(x, y, color='red', linewidth=3) uses color='red' and linewidth=3, which is correct syntax.

3. Final Answer:

   plt.plot(x, y, color='red', linewidth=3) -> Option A

4. Quick Check:

   Correct parameter names and types = plt.plot(x, y, color='red', linewidth=3) [OK]

Hint: Use color='colorname' and linewidth=number [OK]

Common Mistakes:

• Swapping color and linewidth values
• Using wrong parameter names like width
• Passing numbers as color

3. What will be the color and thickness of the line drawn by this code?

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
plt.plot(x, y, color='green', linewidth=5)
plt.show()

medium

A. Blue line with thickness 5

B. Green line with thickness 1

C. Green line with thickness 5

D. Red line with thickness 5

Solution

1. Step 1: Analyze color parameter

   The code sets color='green', so the line color is green.

2. Step 2: Analyze linewidth parameter

   The code sets linewidth=5, so the line thickness is 5 (thicker than default).

3. Final Answer:

   Green line with thickness 5 -> Option C

4. Quick Check:

   color='green' and linewidth=5 = Green line with thickness 5 [OK]

Hint: Check color and linewidth values directly in plot() [OK]

Common Mistakes:

• Ignoring linewidth value
• Assuming default thickness
• Confusing color names

4. Identify the error in this code snippet:

import matplotlib.pyplot as plt
plt.plot([1,2,3], [4,5,6], color=5, linewidth='thick')
plt.show()

medium

A. Missing plt.show() call

B. color should be a number, linewidth should be a string

C. color and linewidth parameters are correct

D. color should be a string, linewidth should be a number

Solution

1. Step 1: Check color parameter type

   color must be a color name string or code, not a number like 5.

2. Step 2: Check linewidth parameter type

   linewidth must be a number (int or float), not a string like 'thick'.

3. Final Answer:

   color should be a string, linewidth should be a number -> Option D

4. Quick Check:

   Parameter types must match expected types [OK]

Hint: color='name', linewidth=number; no numbers for color [OK]

Common Mistakes:

• Passing numbers as color
• Passing strings as linewidth
• Ignoring type errors

5. You want to plot two lines on the same graph: one thick blue line and one thin orange line. Which code correctly does this?

hard

A. plt.plot(x, y1, color='blue', linewidth=6)
plt.plot(x, y2, color='orange', linewidth=1)

B. plt.plot(x, y1, color='orange', linewidth=6)
plt.plot(x, y2, color='blue', linewidth=1)

C. plt.plot(x, y1, linewidth='thick', color='blue')
plt.plot(x, y2, linewidth='thin', color='orange')

D. plt.plot(x, y1, color=6, linewidth='blue')
plt.plot(x, y2, color=1, linewidth='orange')

Solution

1. Step 1: Match colors to lines

   The thick line should be blue, so color='blue' with large linewidth for y1.

2. Step 2: Match thickness and color for second line

   The thin line should be orange, so color='orange' with small linewidth for y2.

3. Step 3: Validate parameter types

   plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) uses correct parameter names and types for both lines.

4. Final Answer:

   plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) -> Option A

5. Quick Check:

   Correct colors and linewidths = plt.plot(x, y1, color='blue', linewidth=6) plt.plot(x, y2, color='orange', linewidth=1) [OK]

Hint: Assign color and linewidth clearly for each line [OK]

Common Mistakes:

• Swapping colors and linewidths
• Using strings for linewidth
• Passing numbers as colors