def process(word_list):
    """
    Process word list before forming query

    Removes characters that are not alphanumeric in the
    words of list and returns words concatenated into a
    string with '_' as delimiter

    Parameters:
    word_list: list of words
    
    Returns:
    string: concatenated words after removing non -alphanum
    with '_' delimiter
    """
    result = ""
    for word in word_list:
        for char in word:
            if char.isalnum():
                result += char
        result += '_'
    result = result[:-1] # remove last underscore
    return result