How to get n-length Boolean array with conditions on X amount of 'True' values

You could create a generator to do it yourself.

def one_true(length):
    i = 0
    while i < length:
        lst = [False] * length
        lst[i] = True
        yield lst
        i +=1

print(list(one_true(3)))

This seems fairly trivial since your True just needs to "crawl" across the array.

If you want to include a case where they are all False just add yield [False] * length at the end.

def one_true(length):
    i = 0
    while i < length:
        lst = [False] * length
        lst[i] = True
        yield lst
        i +=1
    yield [False] * length

print(list(one_true(3)))

And from your example:

events = ['A', 'B', 'C']
print(list(one_true(len(events))))

Or if you want to be more concise you could use a comprehension with a custom function.

def insert_true(lst, index):
    lst[index] = True
    return lst
events = ['A', 'B', 'C']
length = len(events)
foo = [insert_true([False] * length, i) for i in range(length)]

print(foo)