Find the unique values in a column and then sort them

I have a pandas dataframe. I want to print the unique values of one of its columns in ascending order. This is how I am doing it:

import pandas as pd
df = pd.DataFrame({'A':[1,1,3,2,6,2,8]})
a = df['A'].unique()
print a.sort()

The problem is that I am getting a None for the output.