Fig, ax = plt.subplots pattern in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What does this code output?

Consider the following code using plt.subplots(). What will be the type of ax?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
print(type(ax))

A <class 'tuple'>

B <class 'matplotlib.axes._subplots.AxesSubplot'>

C <class 'list'>

D <class 'matplotlib.figure.Figure'>

💡 Hint

Remember that plt.subplots() returns a figure and axes object.

The plt.subplots() function returns a tuple: the first element is a Figure object, and the second is an AxesSubplot object representing the plot area.

❓ data_output

intermediate

How many axes are created?

What is the shape and type of ax after running this code?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots(2, 3)
print(type(ax))
print(ax.shape)

A numpy.ndarray with shape (2, 3)

B list with length 6

C tuple with 2 elements

D matplotlib.axes._subplots.AxesSubplot with no shape

💡 Hint

When multiple subplots are created, ax is an array of axes.

With plt.subplots(2, 3), ax is a 2x3 numpy array of AxesSubplot objects.

❓ visualization

advanced

Identify the correct subplot layout

Which option shows the correct subplot layout for fig, ax = plt.subplots(1, 4)?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots(1, 4)
for i, axis in enumerate(ax):
    axis.plot([0, 1], [i, i+1])
plt.show()

A Four plots arranged vertically in one column

B Two rows and two columns of plots

C Four plots arranged horizontally in one row

D Single plot only

💡 Hint

The arguments (1, 4) mean 1 row and 4 columns.

The plt.subplots(1, 4) creates one row with four columns of subplots arranged horizontally.

🔧 Debug

advanced

Why does this code raise an error?

What error does this code raise and why?

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax[0].plot([1, 2, 3])

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax[0].plot([1, 2, 3])

A TypeError: 'AxesSubplot' object is not subscriptable

B IndexError: list index out of range

C AttributeError: 'Figure' object has no attribute 'plot'

D No error, plots successfully

💡 Hint

Check the type of ax when only one subplot is created.

When only one subplot is created, ax is a single AxesSubplot object, not a list or array, so indexing it causes a TypeError.

🚀 Application

expert

How to flatten axes array for iteration?

Given fig, ax = plt.subplots(3, 2), which option correctly iterates over all axes to plot a line on each?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots(3, 2)
# Fill in the blank to plot on each axis
for axis in _____:
    axis.plot([0, 1], [1, 2])
plt.show()

A list(ax)

B ax.tolist()

C ax

D ax.flatten()

💡 Hint

The axes array is 2D; flatten it to 1D for simple iteration.

The ax is a 2D numpy array of axes. Using ax.flatten() converts it to a 1D array for easy iteration.