Pyplot interface overview in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Pyplot code?

Look at this code that uses matplotlib.pyplot. What will it show?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.title('Simple Line')
plt.xlabel('X axis')
plt.ylabel('Y axis')
plt.show()

A A line graph with points (1,4), (2,5), (3,6) and labeled axes

B A scatter plot with points (1,4), (2,5), (3,6) but no lines

C A bar chart with bars at 1, 2, 3 with heights 4, 5, 6

D An empty plot with only axis labels

💡 Hint

Remember, plt.plot() draws lines connecting points.

The plt.plot() function draws a line graph connecting the points given by the x and y lists. The labels and title appear as expected.

❓ data_output

intermediate

How many lines are drawn by this Pyplot code?

Count the number of lines that will appear after running this code.

Matplotlib

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

A 2

B 3

C 1

D 0

💡 Hint

Each plt.plot() call adds one line.

There are two plt.plot() calls, so two lines will be drawn on the same plot.

❓ visualization

advanced

What does this Pyplot code visualize?

Examine the code below. What kind of plot will it produce?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.linspace(0, 2 * np.pi, 100)
y = np.sin(x)
plt.plot(x, y)
plt.fill_between(x, y, color='skyblue', alpha=0.5)
plt.title('Sine Wave with Fill')
plt.show()

A A scatter plot of sine values with blue dots

B A sine wave line plot with the area under the curve shaded in blue

C A bar chart showing sine values at discrete points

D A line plot of cosine wave with shaded area

💡 Hint

fill_between colors the area under the curve.

The code plots a sine wave line and shades the area under it with a semi-transparent blue color.

🔧 Debug

advanced

What error does this Pyplot code raise?

Look at this code snippet. What error will it cause when run?

Matplotlib

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

A SyntaxError: invalid syntax

B TypeError: unsupported operand type(s)

C ValueError: x and y must have same first dimension

D No error, plot will display

💡 Hint

Check if the x and y lists have the same length.

The x list has 3 elements but y has only 2, so plt.plot() raises a ValueError about dimension mismatch.

🚀 Application

expert

Which option produces a plot with two subplots side by side?

You want to create two plots side by side using Pyplot. Which code will do this correctly?

A

import matplotlib.pyplot as plt
plt.subplots(2, 1)
plt.plot([1, 2, 3], [4, 5, 6])
plt.plot([1, 2, 3], [6, 5, 4])
plt.show()

B

import matplotlib.pyplot as plt
plt.subplot(2, 1)
plt.plot([1, 2, 3], [4, 5, 6])
plt.subplot(2, 2)
plt.plot([1, 2, 3], [6, 5, 4])
plt.show()

C

import matplotlib.pyplot as plt
fig, axs = plt.subplots(2)
axs[0].plot([1, 2, 3], [4, 5, 6])
axs[1].plot([1, 2, 3], [6, 5, 4])
plt.show()

D

import matplotlib.pyplot as plt
fig, axs = plt.subplots(1, 2)
axs[0].plot([1, 2, 3], [4, 5, 6])
axs[1].plot([1, 2, 3], [6, 5, 4])
plt.show()

💡 Hint

Use plt.subplots(rows, columns) to create a grid of plots.

Option D correctly creates a figure with 1 row and 2 columns of subplots, then plots on each axis separately.

Practice

1. What is the main purpose of the plt.show() function in matplotlib's Pyplot interface?

easy

A. To create a new figure object

B. To save the plot as an image file

C. To clear the current plot

D. To display the created plot on the screen

Solution

1. Step 1: Understand the role of plt.show()

   This function is used to display all the figures and plots that have been created so far.

2. Step 2: Differentiate from other functions

   Functions like plt.savefig() save images, and plt.clf() clears plots, but plt.show() actually opens the window to view the plot.

3. Final Answer:

   To display the created plot on the screen -> Option D

4. Quick Check:

   Display plot = plt.show() [OK]

Hint: Remember: plt.show() always displays your plot [OK]

Common Mistakes:

• Confusing plt.show() with plt.savefig()
• Thinking plt.show() clears the plot
• Assuming plt.show() creates a new plot

2. Which of the following is the correct way to import the Pyplot interface from matplotlib?

easy

A. import matplotlib.pyplot as plt

B. import pyplot.matplotlib as plt

C. from matplotlib import plot as plt

D. import matplotlib.pyplot

Solution

1. Step 1: Recall the standard import syntax

   The common and recommended way is to import pyplot from matplotlib and alias it as plt for easy use.

2. Step 2: Check each option

   Only import matplotlib.pyplot as plt is syntactically correct and widely used.

3. Final Answer:

   import matplotlib.pyplot as plt -> Option A

4. Quick Check:

   Standard import = import matplotlib.pyplot as plt [OK]

Hint: Always import pyplot as plt for convenience [OK]

Common Mistakes:

• Swapping module and submodule names
• Using incorrect alias names
• Missing 'as plt' alias

3. What will be the output of the following code?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.title('Sample Plot')
plt.show()

medium

A. A line plot with points (1,4), (2,5), (3,6) and title 'Sample Plot' displayed

B. A scatter plot with points (1,4), (2,5), (3,6) without any title

C. No plot will be shown because plt.show() is missing

D. An error because plt.title() is not a valid function

Solution

1. Step 1: Analyze the plot function

   plt.plot() with two lists creates a line plot connecting points (1,4), (2,5), and (3,6).

2. Step 2: Check the title and show functions

   plt.title('Sample Plot') adds the title, and plt.show() displays the plot window.

3. Final Answer:

   A line plot with points (1,4), (2,5), (3,6) and title 'Sample Plot' displayed -> Option A

4. Quick Check:

   plt.plot + plt.title + plt.show = line plot with title [OK]

Hint: plt.plot draws lines; plt.show displays them [OK]

Common Mistakes:

• Confusing plt.plot with scatter plot
• Forgetting plt.show() to display plot
• Assuming plt.title() is invalid

4. Identify the error in the following code snippet:

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

medium

A. plt.show() is missing, so plot won't display

B. plt.plot() requires only one list, so two lists cause a syntax error

C. The x and y data lists have different lengths causing a ValueError

D. No error; the plot will display correctly

Solution

1. Step 1: Check the lengths of x and y data

   The x list has 3 elements, but the y list has only 2 elements, which is invalid for plotting.

2. Step 2: Understand the error raised

   This mismatch causes a ValueError because each x must have a corresponding y value.

3. Final Answer:

   The x and y data lists have different lengths causing a ValueError -> Option C

4. Quick Check:

   Length mismatch in plt.plot = ValueError [OK]

Hint: x and y lists must be same length in plt.plot [OK]

Common Mistakes:

• Assuming plt.plot accepts different length lists
• Thinking plt.show() is missing
• Believing two lists cause syntax error

5. You want to create a plot with two lines on the same figure using Pyplot. Which code snippet correctly does this?

hard

A. import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.clear()
plt.plot([1, 2, 3], [6, 5, 4])
plt.show()

B. import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.plot([1, 2, 3], [6, 5, 4])
plt.show()

C. import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.show()
plt.show()

D. import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.show()
plt.plot([1, 2, 3], [6, 5, 4])

Solution

1. Step 1: Understand how to plot multiple lines

   Calling plt.plot() multiple times before plt.show() adds multiple lines to the same figure.

2. Step 2: Check each option for correct sequence

   import matplotlib.pyplot as plt plt.plot([1, 2, 3], [4, 5, 6]) plt.plot([1, 2, 3], [6, 5, 4]) plt.show() calls both plot commands before a single show, so both lines appear together. Others either call show too early or clear the plot.

3. Final Answer:

   import matplotlib.pyplot as plt plt.plot([1, 2, 3], [4, 5, 6]) plt.plot([1, 2, 3], [6, 5, 4]) plt.show() -> Option B

4. Quick Check:

   Multiple plt.plot calls before plt.show = multiple lines [OK]

Hint: Plot all lines before plt.show() to display together [OK]

Common Mistakes:

• Calling plt.show() too early clears previous plots
• Using plt.clear() removes existing plots
• Expecting multiple plt.show() calls to overlay plots