Figure creation with plt.figure in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the size of the figure created?

Consider the following code snippet using matplotlib:

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(8, 4))
print(fig.get_size_inches())

What will be the output of this code?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(8, 4))
print(fig.get_size_inches())

A [8. 4.]

B [4. 8.]

C [0 0]

D Error: AttributeError

💡 Hint

The figsize parameter sets the width and height in inches.

The figsize argument in plt.figure sets the width and height of the figure in inches. The get_size_inches() method returns these dimensions as a numpy array.

❓ data_output

intermediate

How many axes are in the figure?

Given this code:

import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)
print(len(fig.axes))

What is the printed output?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)
print(len(fig.axes))

A 1

B Error: AttributeError

C 0

D 2

💡 Hint

Each add_subplot call adds one axes to the figure.

The figure has two subplots added, so fig.axes contains two Axes objects.

❓ visualization

advanced

What does the figure look like?

Examine this code:

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(6, 3))
ax = fig.add_axes([0.1, 0.1, 0.8, 0.8])
ax.plot([1, 2, 3], [4, 5, 6])
plt.show()

Which description best matches the figure displayed?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(6, 3))
ax = fig.add_axes([0.1, 0.1, 0.8, 0.8])
ax.plot([1, 2, 3], [4, 5, 6])
plt.show()

A A tall square figure with two side-by-side plots.

B A figure with multiple overlapping plots.

C A wide rectangular figure with a single plot filling most of the area.

D A small figure with no plots visible.

💡 Hint

figsize sets width and height; add_axes controls plot position and size.

The figure is 6 inches wide and 3 inches tall, making it wide and short. The axes fill 80% width and height starting at 10% from left and bottom, so the plot fills most of the figure.

🔧 Debug

advanced

Why does this code raise an error?

Look at this code:

import matplotlib.pyplot as plt
fig = plt.figure(figsize=8, 4)
ax = fig.add_subplot(111)
plt.show()

Why does it raise an error?

Matplotlib

import matplotlib.pyplot as plt
fig = plt.figure(figsize=8, 4)
ax = fig.add_subplot(111)
plt.show()

A Because figsize must be a tuple, not two separate arguments.

B Because add_subplot(111) is invalid syntax.

C Because plt.show() must be called before creating the figure.

D Because matplotlib is not imported correctly.

💡 Hint

Check the syntax of figsize parameter.

figsize expects a single tuple argument like (8, 4). Passing two separate arguments causes a TypeError.

🚀 Application

expert

How to create two figures with different sizes?

You want to create two separate figures with sizes 5x5 and 10x2 inches respectively. Which code correctly creates these figures and prints their sizes?

Matplotlib

import matplotlib.pyplot as plt
fig1 = plt.figure(figsize=(5, 5))
fig2 = plt.figure(figsize=(10, 2))
print(fig1.get_size_inches())
print(fig2.get_size_inches())

A

fig1 = plt.figure(figsize=5, 5)
fig2 = plt.figure(figsize=10, 2)
print(fig1.get_size_inches())
print(fig2.get_size_inches())

B

fig1 = plt.figure(figsize=(5, 5))
fig2 = plt.figure(figsize=(10, 2))
print(fig1.get_size_inches())
print(fig2.get_size_inches())

C

fig1 = plt.figure(figsize=[5, 5])
fig2 = plt.figure(figsize=[10, 2])
print(fig1.get_size_inches())
print(fig2.get_size_inches())

D

fig1 = plt.figure(figsize=(5))
fig2 = plt.figure(figsize=(10))
print(fig1.get_size_inches())
print(fig2.get_size_inches())

💡 Hint

figsize must be a tuple of two numbers.

Only option B correctly passes figsize as tuples. Option B passes separate arguments causing error. Option B uses list instead of tuple (works but not recommended). Option B passes single values creating square figures.

Practice

1. What does the plt.figure() function do in matplotlib?

easy

A. Plots a line graph directly

B. Creates a new blank canvas for plotting graphs

C. Saves the current plot to a file

D. Displays the plot on the screen

Solution

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

   The plt.figure() function creates a new empty figure, which is like a blank canvas for drawing plots.

2. Step 2: Differentiate from other functions

   Functions like plt.plot() draw on the figure, plt.show() displays it, and plt.savefig() saves it. Only plt.figure() creates the blank space.

3. Final Answer:

   Creates a new blank canvas for plotting graphs -> Option B

4. Quick Check:

   plt.figure() = new blank canvas [OK]

Hint: Remember: figure = blank canvas for plots [OK]

Common Mistakes:

• Confusing plt.figure() with plt.plot()
• Thinking plt.figure() displays the plot
• Assuming plt.figure() saves the plot

2. Which of the following is the correct way to create a figure with size 8 inches wide and 6 inches tall using plt.figure()?

easy

A. plt.figure(size=(8, 6))

B. plt.figure(dimensions=(8, 6))

C. plt.figure(size=[8, 6])

D. plt.figure(figsize=(8, 6))

Solution

1. Step 1: Recall the correct parameter name

   The parameter to set figure size is figsize, which takes a tuple of (width, height) in inches.

2. Step 2: Check the syntax of options

   Only plt.figure(figsize=(8, 6)) uses figsize=(8, 6) correctly. Others use wrong parameter names or data types.

3. Final Answer:

   plt.figure(figsize=(8, 6)) -> Option D

4. Quick Check:

   figsize=(width, height) = plt.figure(figsize=(8, 6)) [OK]

Hint: Use figsize=(width, height) tuple inside plt.figure() [OK]

Common Mistakes:

• Using 'size' instead of 'figsize'
• Passing list instead of tuple
• Using wrong parameter names like 'dimensions'

3. What will be the output of this code?

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(4, 3), dpi=100)
print(fig.get_size_inches())
print(fig.dpi)

medium

A. [4 3]
100.0

B. [400 300]
100.0

C. [4. 3.]
100.0

D. [4.0 3.0]
10

Solution

1. Step 1: Understand figsize and dpi

   The figsize is in inches as a float array, so fig.get_size_inches() returns [4. 3.]. The dpi is dots per inch, set to 100.0.

2. Step 2: Check print outputs

   Printing fig.get_size_inches() shows floats with decimal points. Printing fig.dpi shows 100.0 as set.

3. Final Answer:

   [4. 3.] 100.0 -> Option C

4. Quick Check:

   figsize floats and dpi number = [4. 3.] and 100.0 [OK]

Hint: fig.get_size_inches() returns floats, dpi is float [OK]

Common Mistakes:

• Expecting integers instead of floats for size
• Confusing dpi value with size
• Misreading output format

4. Identify the error in this code snippet:

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

medium

A. The parameter 'size' is invalid; should be 'figsize'

B. plt.plot() cannot be used after plt.figure()

C. plt.show() is missing parentheses

D. The lists in plt.plot() have different lengths

Solution

1. Step 1: Check parameter names in plt.figure()

   The correct parameter to set figure size is figsize, not size. Using size causes an error.

2. Step 2: Verify other parts of the code

   Using plt.plot() after plt.figure() is valid. plt.show() has parentheses. Lists have same length.

3. Final Answer:

   The parameter 'size' is invalid; should be 'figsize' -> Option A

4. Quick Check:

   Use figsize= not size= in plt.figure() [OK]

Hint: Use figsize=, not size=, to set figure size [OK]

Common Mistakes:

• Using 'size' instead of 'figsize'
• Thinking plt.plot() can't follow plt.figure()
• Forgetting parentheses in plt.show()

5. You want to create two separate plots in two separate windows. Which code correctly creates two figures and plots a simple line in each?

hard

A. fig1 = plt.figure(figsize=(4,3))
plt.plot([1,2,3],[4,5,6])
fig2 = plt.figure(figsize=(4,3))
plt.plot([1,2,3],[6,5,4])
plt.show()

B. plt.figure(figsize=(8,3))
plt.subplot(1,2,1)
plt.plot([1,2,3],[4,5,6])
plt.subplot(1,2,2)
plt.plot([1,2,3],[6,5,4])
plt.show()

C. fig = plt.figure(figsize=(8,3))
plt.plot([1,2,3],[4,5,6])
plt.plot([1,2,3],[6,5,4])
plt.show()

D. plt.figure(figsize=(4,3))
plt.plot([1,2,3],[4,5,6])
plt.figure(figsize=(4,3))
plt.plot([1,2,3],[6,5,4])

Solution

1. Step 1: Understand figure creation for multiple plots

   Creating two separate figures requires calling plt.figure() twice, each time creating a new blank canvas.

2. Step 2: Check code correctness

   fig1 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) fig2 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) plt.show() creates two figures with specified sizes and plots on each before showing. plt.figure(figsize=(8,3)) plt.subplot(1,2,1) plt.plot([1,2,3],[4,5,6]) plt.subplot(1,2,2) plt.plot([1,2,3],[6,5,4]) plt.show() uses subplots in one figure, not two figures. fig = plt.figure(figsize=(8,3)) plt.plot([1,2,3],[4,5,6]) plt.plot([1,2,3],[6,5,4]) plt.show() plots both lines on one figure. plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) misses plt.show().

3. Final Answer:

   fig1 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) fig2 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) plt.show() -> Option A

4. Quick Check:

   Two plt.figure() calls = two separate plots [OK]

Hint: Call plt.figure() twice for separate plot windows [OK]

Common Mistakes:

• Using subplots instead of separate figures
• Plotting multiple lines on one figure expecting separate windows
• Forgetting plt.show() to display plots