Summing list of counters in python

Question

I am looking to sum a list of counters in python. For example to sum:

counter_list = [Counter({\"a\":1, \"b\":2}), Counter({\"b\":3, \"c\":4})]

Answer 1

The sum function has the optional start argument which defaults to 0. Quoting the linked page:

sum(iterable[, start])

Sums start and the items of an iterable from left to right and returns the total

Set start to (empty) Counter object to avoid the TypeError:

In [5]: sum(counter_list, Counter())
Out[5]: Counter({'b': 5, 'c': 4, 'a': 1})