def char_count(text):
    """ counts the number of occurances of ascii letters -
    65<=ord(ch)<=90 (capital) or 97<=ord(ch)<=122, in a text.
    Returns a list of pairs, where first elements in pairs are the
    lower case letters, and second elements being the counts """
    
    d = {}  # initializing an empty dictionary
    for ch in text:
        ch=str.lower(ch)        
        if ord(ch)<ord("a") or ord(ch)>ord("z"):  # not a letter
            continue
        else:    # incrementing letter count by 1
            if ch in d: 
                d[ch]=d[ch]+1
            else:
                d[ch]=1

    lst=list(d.items())  # truning dictionary into list
    return sorted(lst, key=lambda pair: pair[1], reverse=True) # sort high to low by counts
#    return sorted(lst, key=lambda pair: -pair[1]) # sort high to low by counts