DataFrame调用其他列内容，新建一列的两种方法，apply更高效

# Import cars data

import pandas as pd

cars = pd.read_csv('cars.csv', index_col = 0)

# Use .apply(str.upper)

#for lab, row in cars.iterrows() :

　　#cars.loc[lab, "COUNTRY"] = row["country"].upper()

cars['COUNTRY'] = cars['country'].apply(str.upper)

print(cars)