วันที่ก่อสร้างเสร็จเมื่อใดคือ greifswald - 4 (kgr 4)
What was the date that construction was finished when the unit was greifswald - 4 (kgr 4)?
df = pd.DataFrame(columns=['finish_construction', 'unit'])
df.loc[df['unit'] == 'greifswald - 4 (kgr 4)', 'finish_construction']