import topotoolbox
import matplotlib.pyplot as plt
dem = topotoolbox.load_dem('perfectworld')
fd = topotoolbox.FlowObject(dem)
s = topotoolbox.StreamObject(fd,threshold=1000,units='pixels')
fig, ax = plt.subplots()
_= dem.plot(cmap="terrain")
_= s.plot(color='r')
plt.show()