Python pandas: flag duplicate rows

As per the docs use the keep argument and set as False. As you can see it defaults to first.

import pandas as pd

df = pd.DataFrame({'Column_A': ['AAA', 'AAB', 'AAB', 'AAC']})
df['duplicate'] = df.duplicated(keep=False)

print(df)

     Column_A  duplicate
0    'AAA'     False
1    'AAB'     True
2    'AAB'     True
3    'AAC'     False

I imagine myself lost in the wilderness and all I have to survive is pd.factorize and np.bincount
Please, don't accept this answer

f, u = pd.factorize(df.Column_A.values)
df.assign(duplicate=np.bincount(f)[f] > 1)

  Column_A  duplicate
0      AAA      False
1      ABC       True
2      ABC       True