If and function in pandas

I'm new to python and I'm trying to find some thing like If and elif for my case. My code as below:

import pandas as pd
df = pd.DataFrame({'v_contract_number': ['VN120001438','VN120001439',
                                          'VN120001440','VN120001438',
                                          'VN120001439','VN120001440'],
                                            'Collateral': ['Real Estate','Real Estate','Gold','Gold','Deposit','Deposit'],
                                        'Purpose': [20,30,20,30,20,30]})

# df
    v_contract_number   Collateral  Purpose
0   VN120001438 Real Estate 20
1   VN120001439 Real Estate 30
2   VN120001440 Gold    20
3   VN120001438 Gold    30
4   VN120001439 Deposit 20

cols = ['Collateral', 'Purpose']
df['combined'] = df[cols].apply(lambda row: '_'.join(row.values.astype(str)), axis=1)
df['v_purpose'] = df['combined'].apply(lambda x:'Real Estate Loan' if x == "Real Estate_20" else 'Others')
df.head()

#df
v_contract_number   Collateral  Purpose combined    v_purpose
0   VN120001438 Real Estate 20  Real Estate_20  Real Estate Loan
1   VN120001439 Real Estate 30  Real Estate_30  Others
2   VN120001440 Gold    20  Gold_20 Others
3   VN120001438 Gold    30  Gold_30 Others
4   VN120001439 Deposit 20  Deposit_20  Others

But I want to add more conditions to combined column like:

if df['combined'] == "Real Estate_20":
   df['v_purpose'] == "Real Estate Loan"
elif df['combined'] == "Real Estate_30":
   df['v_purpose'] == "Home Mortgage Loan"
else
   df['v_purpose'] == "Others"

Thank for your help