if len(beats) > 1:
# do plotting
- from numpy import array, arange, mean, median, diff
+ from numpy import mean, median, diff
import matplotlib.pyplot as plt
bpms = 60./ diff(beats)
print 'mean period:', "%.2f" % mean(bpms), 'bpm', 'median', "%.2f" % median(bpms), 'bpm'