example_defaultdict.py

"""
I want to loop through a file that contains:
Rv0001  10
Rv0001  20
Rv0002  50
Rv0003  70

and I want something that looks like this:
{
    "Rv0001": [10,20],
    "Rv0002": [50],
    "Rv0003": [70]
}
"""

# Solution 1
results = {}
for line in open("file.txt"):
    row = lines.strip().split()
    if row[0] not in results:
        results[row[0]] = []
    results[row[0]].append(int(row[1]))

# Solution 2 with defaultcdict
results = defaultdict(list)
for line in open("file.txt"):
    row = lines.strip().split()
    results[row[0]].append(int(row[1]))