How to check if an element is an empty list in pandas?

You can do this:

df[df["col"].str.len() != 0]

Example:

import pandas as pd

df = pd.DataFrame({"col": [[1], [2, 3], [], [4, 5, 6], []]}, dtype=object)
print(df[df["col"].str.len() != 0])
#          col
# 0        [1]
# 1     [2, 3]
# 3  [4, 5, 6]