extract column value based on another column pandas dataframe

pandas.py

import pandas as pd

file1 = pd.read_csv('./n/oregonhie_descriptive_vars.csv')

file2 = pd.read_csv('./n/oregonhie_inperson_vars.csv')

file2['treatment'] = file2['person_id']

def proccess(key):
	a = file1.loc[file1['person_id'] == key, 'treatment'].iloc[0]
	return a
	
file2['treatment']= file2['treatment'].apply(proccess)

file2.to_csv('output.csv', encoding='utf-8')