How to conditionally concat 2 columns in Python Pandas Dataframe

I have the following dataframe:

d = {'col1': [1, "Avoid", 3, "Avoid"], 'col2': ["AA", "BB", "Avoid", "Avoid"]}
df = pd.DataFrame(data=d)
df

    col1    col2
0   1       AA
1   Avoid   BB
2   3       Avoid
3   Avoid   Avoid

I have to conditionally concat col1 and col2 into col3. Conditions:

• Only concat 2 columns as long as none of them is Avoid.
• If any of col1 and col2 is Avoid, col3 will be equal to Avoid as well.
• When performing concatination, " & " needs to be added between column values in col3. For instance, first row of col3 will be "1 & AA".

The end result is supposed to look as the following:

    col1    col2    col3
0   1       AA      1 & AA
1   Avoid   BB      Avoid
2   3       Avoid   Avoid
3   Avoid   Avoid   Avoid

How can I do this without dealing with for loops?

>Solution :

try this:

df["col3"]=df.apply(lambda x:"Avoid" if x["col1"]=="Avoid" or x["col2"]=="Avoid" else f"{x['col1']} & {x['col2']}",axis=1)