Get the total count of 1 field of a list of namedtuple objects

Question

In Python, what is the easiest way to get the total count of one field from a set of named tuples?

In this example, I'm looking for the total count of TestResults.failed, which should be 4. It's doable with a for loop, but it feels like there could be a more efficient way.

from collections import namedtuple

TestResults = namedtuple('TestResults', ['failed', 'attempted'])

test_results = [
    TestResults(0, 5),
    TestResults(3, 28),
    TestResults(1, 7)
]

failed_count = 0
for r in test_results:
    if hasattr(r, 'failed'):
        failed_count += r.failed

print(failed_count)

Answer 1

With arbitrary objects, you can use getattr with 0 as a default value, and use sum with a generator expression:

sum(getattr(res, 'failed', 0) for res in test_results)

Since you have namedtuples with no optional values, you can get the values directly using dot notation:

sum(res.failed for res in test_results)

If you have a namedtuple with an optional 'failed' field, if the optional value is 0, then the above should work, otherwise, if the optional value is None, you could use this to use 0 as a default value:

sum(res.failed or 0 for res in test_results)