Cannot use seaborn style with matplotlib

[Layla-Aphrodite]

When I try to use the seaborn style the same way as example showed on the book Python Crash Course:

import matplotlib.pyplot as plt

input_values  =  [1,2,3,4,5]
squares = [1,4,9,16,25]

plt.style.use('seaborn')
fig, ax = plt.subplots()
---snip---

it blew up with the following warning:
OSError: 'seaborn' is not a valid package style, path of style file, URL of style file, or library style name (library styles are listed in style.available)

And when I try to see the full list of available styles running the following line in terminal, the output is: -bash: import: command not found.
>>> import matplotlib.pyplot as plt

Does anyone know the reason why?