Date    ID  Name    Company     Email
2018    1   AB      Apple       apple@apple.com
2017    2   BC      MicroSoft   ms@ms.com
2016    3   CD      Amazon      amz@amz.com

code    company_name    product
123     MicroSoft       Windows
456     Apple           iphone
789     Amazon          cloud

def finder(slave, master):
    finalList = []
    for company in slave['Company']:
        if type(company) == 'some_specific_type':
            for info in master['company_name']:
                if company in info:
                    finalList.append(master.loc[str(info)]['code'])
                    break
        else:
            finalList.append(company)
    return finalList

slave['newCode'] = finder(slave, master) // very slow

Date    ID  Name    Company     Email               newCode
2018    1   AB      Apple       apple@apple.com     456
2017    2   BC      MicroSoft   ms@ms.com           123
2016    3   CD      Amazon      amz@amz.com         789

foundList = slave.merge(master, how='inner',
                        left_on='Company',
                        right_on='company_name')['Company']
#0        Apple
#1    MicroSoft
#2       Amazon