def find_largest_true_block(arr):
    """
    Given a boolean numpy array, finds the starting and ending indices
    for the largest continuous block of """
    start_index = -1
    max_start_index = -1
    max_length = -1
    length = -1
    i = 0
    is_in_block = False
    while i < len(arr):
        if arr[i] and not is_in_block:
            start_index = i
            length = 0
            is_in_block = True
        elif arr[i] and is_in_block:
            length += 1
        else:
            is_in_block = False
            if length > max_length:
                max_length = length
                max_start_index = start_index
        i += 1
    if length > max_length:
        max_length = length
        max_start_index = start_index
    return max_start_index, max_start_index + max_length