def linear_search(sequence, target):
    """Pure implementation of linear search algorithm in Python

    :param sequence: some sorted collection with comparable items
    :param target: item value to search
    :return: index of found item or None if item is not found

    Examples:
    >>> linear_search([0, 5, 7, 10, 15], 0)
    0

    >>> linear_search([0, 5, 7, 10, 15], 15)
    4

    >>> linear_search([0, 5, 7, 10, 15], 5)
    1

    >>> linear_search([0, 5, 7, 10, 15], 6)

    """
    for index, item in enumerate(sequence):
        if item == target:
            return index
    return None