Pandas: TypeError: sort_values() missing 1 required positional argument: 'by'

I am facing TypeError: sort_values() missing 1 required positional argument: 'by'

for i in range(0,len(data_sims.index)):for j in range(1,len(data_sims.columns)):    user = data_sims.index[i]    serial = data_sims.columns[j]    if dataUser.ix[i][j] == 1:        data_sims.ix[i][j] = 0    else:        serial_top_names = data_neighbours.ix[serial][1:10]        serial_top_sims = dataSim.ix[serial].sort_values(ascending=False)[1:10]        user_preferences = dataUser.ix[user,serial_top_names]        data_sims.ix[i][j] = getScore(user_preferences,serial_top_sims)

Detailed Error:

> ---------------------------------------------------------------------------TypeError                                 Traceback (most recent call last) in ()      9         else:     10             serial_top_names = data_neighbours.ix[serial][1:10]---> 11             serial_top_sims = dataSim.ix[serial].sort_values(ascending=False)[1:10]     12             user_preferences = dataUser.ix[user,serial_top_names]     13 TypeError: sort_values() missing 1 required positional argument: 'by'

I tried using following but didn't work

pd.DataFrame.sort_values(dataSim,ascending=[0])[1:10]

Is there anything that I'm missing?