I know that if I change the linewidth of a line, that is automatically updated in the legend. However I would like to just change the legend linewidth without affecting the plot.
Here's a simple example of how to do it:
import numpy as np
import matplotlib.pyplot as plt
# make some data
x = np.linspace(0, 2*np.pi)
y1 = np.sin(x)
y2 = np.cos(x)
# plot sin(x) and cos(x)
p1 = plt.plot(x, y1, 'b-', linewidth=1.0)
p2 = plt.plot(x, y2, 'r-', linewidth=1.0)
# make a legend for both plots
leg = plt.legend([p1, p2], ['sin(x)', 'cos(x)'], loc=1)
# set the linewidth of each legend object
for legobj in leg.legendHandles:
legobj.set_linewidth(2.0)
plt.show()