The pyplot interface

plt.plot talks to the current Axes. That is convenient for one figure. Several calls in a row still draw on the same Axes until you make a new figure.

One Axes, several calls

x = np.linspace(0, 2 * np.pi, 80)
plt.plot(x, np.sin(x), label="sin")
plt.plot(x, np.cos(x), label="cos")
print("current Axes:", plt.gca())
plt.legend()
plt.show()

plt.gca() is “get current Axes”.

A second figure

x = np.linspace(0, 4, 50)
plt.figure()
plt.plot(x, x)
plt.title("linear")
plt.figure()
plt.plot(x, x ** 2)
plt.title("quadratic")
plt.show()

Each plt.figure() starts a new canvas. Both appear after one plt.show().

Why the next chapter exists

x = np.linspace(0, 2 * np.pi, 80)
plt.plot(x, np.sin(x))
plt.title("first")
plt.plot(x, np.cos(x))
plt.title("oops — still the same Axes")
plt.show()

The second plot added a line to the same Axes and overwrote the title. fig, ax = plt.subplots() (next chapter) names the Axes you mean.