Importing Matplotlib

I am new to Python and I am learning matplotlib. I am following the video tutorial recommended in the official User Manual of matplotlib: 'Plotting with matplotlib' by Mike Muller. The instructor does not show how he imports matplotlib but proceeds instantly with commands such as plot(x, linear, x, square), where x a sequence he has defined.

I tried to run

import matplotlib 
from matplotlib import pyplot as plt
import numpy as np
import pandas as pd
x = np.arange(100)
lines = plot(x, 'linear', 'g:+', x, 'square','r-o')

and got the error

NameError: name 'plot' is not defined

Short answer

You need to prefix all plotting calls with plt. like

lines = plt.plot(x, 'linear', 'g:+', x, 'square','r-o')

Longer answer

In Python functions that are not "builtin", i.e. always present, must be imported from modules. In this case the line

from matplotlib import pyplot as plt

is the same as

import matplotlib.pyplot as plt

and means that you are importing the pyplot module of matplotlib into your namespace under the shorter name plt. The pyplot module is where the plot(), scatter(), and other commands live.

If you don't want to write plt. before every plot call you could instead do

from matplotlib.pyplot import *

which will import all functions (symbols) into the global namespace, and you can now use your original line:

lines = plot(x, 'linear', 'g:+', x, 'square','r-o')