def EventHist(db,dk):  #db is a Shelve object of pandas dataframes, dk is a list of keys
    for dbKey in dk:
        hist,bins=fn(db[dbKey])   # this function is only thing that changes by event
        plt.semilogx(hist,bins,label=dbKey)
        db.sync()
    # bunch of other plot properties
    plt.show()

@EventHist
def myEvent(df):
    return np.hist(df['foo'].values+df['bar'].values)