def occurrences(s):
    s = s.lower()
    dletter = {}
    for c in s:
        if c.isalpha() or c.isdigit():
            if c in dletter:
                dletter[c] = dletter[c] + 1
            else:
                dletter[c] = 1
    return dletter

def vowel_occurrences(s):
    s = s.lower()
    dvowel = {}
    for vowel in 'aeiou':
        dvowel[vowel] = 0
    ## dvowel may be inicialized direcly
    ## dvowel ={'a':0,'e':0,'i':0,'o':0,'u':0}
    for char in s:
        if char in 'aeiou':
            dvowel[char] = dvowel[char] + 1 
    return dvowel