how to count the number of unique values appeared in python code example

Example 1: counting unique values python

df.loc[df['mID']=='A','hID'].agg(['nunique','count','size'])

Example 2: python count unique values in list

len(set(["word1", "word1", "word2", "word3"]))
# set is like a list but it removes duplicates
# len counts the number of things inside the set