I want to do something like this:

```
for row in df:
if row['Country'] == 'unknown':
    row['Country'] = city2country_mapping[row['city']]

```

Country and City are columns.

'city2country\_mapping' is a dictionary where key:value pair is 'city':'country'.

(basically i'm trying to fill in the unknowns by getting country from dictionary as i know city for each row)