print() 
bins = np.array([0, 1, 10, 60, 60 * 10, 60 * 60, 24 * 60 * 60])
print('hisogram bins:', bins)
y, x = np.histogram(df, bins=bins, normed=True)
x = x[1:]
hist = pd.Series(y, x)
ax = hist.plot(kind='bar', width=1, alpha=0.5, align='center')
ax.set_title('Non-Uniform Bin Histogram')
ax.set_xlabel('Time Length')
ax.set_xticklabels(['1 s', '10 s', '1 Min', '1 Hr', '1 Day', '>1 Day'],
    rotation='horizontal')
pandas histogram with logarithmic axes