Exercise for reference: 

Create a script that uses the attached countries_by_area.txt  file as a data source and prints out the top 5 most densely populated countries.

Answer: 

import pandas

data = pandas.read_csv("countries_by_area.txt")
data["density"] = data["population_2013"] / data["area_sqkm"]
data = data.sort_values(by="density", ascending=False)

for index, row in data[:5].iterrows():
    print(row["country"])

Explanation:

We're using pandas to load the data as a dataframe and then calculate a density column in line 4. Then we use sort_values  to sort the data by density in descending order. Lastly, in the last two lines, we access the first 5 rows of the dataframe and iterate using iterrows .