Thank's a lot for your answers, you help me !

I use this code :

result=[]
for i, j in itertools.combinations(df["PORT CODE"], 2):
    if i!=i+1:
    result.append(f'{i}_{j}')
    dff=pd.DataFrame(result)

I need you for the next step :

First column is the Port and the 2nd the service.

I want concatenate i and i+1 if the service is different. In this case, the result is :