How to do it...

The following block of code along with comments helps you to understand the process of changing and resetting default environment variables: 

1. Import the matplotlib.pyplot package with the plt synonym:

import matplotlib.pyplot as plt

2. Load x and y variables from same test.csv file that we used in the preceding recipe:

x, y = np.loadtxt ('test.csv', unpack = True, usecols = (0,1), 
                    delimiter = ',')

3. Change the default values for multiple parameters within the group 'lines':

matplotlib.rc('lines', linewidth=4, linestyle='-', marker='*')

4. Change the default values for parameters individually:

matplotlib.rcParams['lines.markersize'] = 20
matplotlib.rcParams['font.size'] = '15.0'

5. Plot the graph:

plt.plot(x,y)

6. Display the graph:

plt.show()

The following is the output that will be obtained: