How to create a list in Python with the unique values of a CSV file?

Question

I have CSV file that looks like the following,

1994, Category1, Something Happened 1
1994, Category2, Something Happened 2
1995, Category1, Something Happen         


        

Answer 1

dawg pointed out one of the greatest tricks in Python: using set() to remove duplicates from a list. dawg shows how to build the unique list from scratch by adding each item to a set, which is perfect. But here's another equivalent way to do it, generating a list with duplicates and a list without duplicates using a list(set()) approach:

import csv

in_str = [
    'year, category, event',
    '1994, Category1, Something Happened 1',
    '1994, Category2, Something Happened 2',
    '1995, Category1, Something Happened 3',
    '1996, Category3, Something Happened 4',
    '1998, Category2, Something Happened 5'
    ]

cdr = csv.DictReader(in_str, skipinitialspace=True)

col = []
for i in cdr:
    col.append(i['category'])

# all items in the column...
print(col)
# only unique items in the column...
print(list(set(col)))