How to count duplicates in Pandas?

Question

I use this pattern to find duplicates in column A from set duplicates :

duplicates = {1, 2, 3}
df[~df['A'].isin(duplicates)]

It works and returns me rows witout duplicates. But how to get count of duplicates?

I have tried these:

df[~df['A'].isin(duplicates)].count()
~df['A'].isin(duplicates).count()

And how to extract this count to variable.

Answer 1

new_df = df[~df['A'].isin(duplicates)]
new_df['duplicate_values'] = new_df.duplicated('A')
new_df['duplicate_values'].sum()