How do I find the duplicates in a list and create another list with them?

Question

How can I find the duplicates in a Python list and create another list of the duplicates? The list only contains integers.

Answer 1

I would do this with pandas, because I use pandas a lot

import pandas as pd
a = [1,2,3,3,3,4,5,6,6,7]
vc = pd.Series(a).value_counts()
vc[vc > 1].index.tolist()

Gives

[3,6]

Probably isn't very efficient, but it sure is less code than a lot of the other answers, so I thought I would contribute