Axes vs pyplot interface comparison in Matplotlib - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of plotting with Axes vs pyplot

What will be the output of the following code snippet comparing Axes and pyplot interfaces?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [4, 5, 6])
plt.plot([1, 2, 3], [6, 5, 4])
print(len(fig.axes))

A 2

B 3

C 0

D 1

💡 Hint

Think about how many axes objects are created and used in the figure.

The code creates one figure and one Axes object with plt.subplots(). The ax.plot() adds a line to that Axes. The plt.plot() call without specifying axes adds a new line to the current axes, which is the same Axes. So only one Axes exists in the figure, but two lines are plotted on it. The length of fig.axes is 1, but the question asks for output of print(len(fig.axes)) which is 1. However, plt.plot() outside of ax adds to the current axes, so no new axes are created. So the output is 1.

❓ Predict Output

intermediate

Number of lines plotted on Axes

After running this code, how many lines are plotted on the Axes object ax?

Matplotlib

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

A 1

B 3

C 2

D 0

💡 Hint

Consider which axes the pyplot plot adds lines to.

Both ax.plot() and plt.plot() add lines to the same Axes object ax because plt.plot() uses the current axes, which is ax here. So ax has two lines plotted.

🔧 Debug

advanced

Identify the error in Axes vs pyplot plotting

What error will this code produce?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
plt.plot([1, 2, 3], [4, 5, 6])
ax.plot([1, 2, 3], [6, 5, 4])
plt.show()
print(len(fig.axes))

A No error, output is 1

B No error, output is 2

C AttributeError: 'NoneType' object has no attribute 'axes'

D TypeError: 'int' object is not callable

💡 Hint

Check if plt.plot() creates new axes or uses existing ones.

plt.plot() uses the current axes, which is ax created by plt.subplots(). So no new axes are created. fig.axes contains one Axes object, so len(fig.axes) is 1. No error occurs.

❓ data_output

advanced

Axes object properties after plotting

After running this code, what is the value of ax.get_lines()[1].get_ydata()?

Matplotlib

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

A [6 5 4]

B [4 5 6]

C [1 2 3]

D IndexError: list index out of range

💡 Hint

Remember plt.plot() adds to the current Axes lines list.

ax.get_lines() returns a list of Line2D objects. The first line plotted is with y data [4,5,6], the second line is from plt.plot() with y data [6,5,4]. So ax.get_lines()[1].get_ydata() returns [6 5 4].

❓ visualization

expert

Visual difference between Axes and pyplot interface

Which option best describes the visual output difference when plotting with Axes.plot() vs pyplot.plot() in this code?

Matplotlib

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [4, 5, 6], label='Axes plot')
plt.plot([1, 2, 3], [6, 5, 4], label='Pyplot plot')
ax.legend()
plt.show()

A One plot with only the 'Axes plot' line visible

B One plot with two lines and a legend showing both labels

C Two separate plots appear in different windows

D One plot with only the 'Pyplot plot' line visible

💡 Hint

Consider how legend and lines are managed on the same Axes.

Both lines are plotted on the same Axes object ax. The legend shows both labels because both lines belong to ax. So the plot shows two lines with a legend listing 'Axes plot' and 'Pyplot plot'.