def get_count(sentence):
    vowels = "aeiou"
    count = 0
    for char in sentence:
        if char in vowels:
            count += 1
    return count


print(get_count("abracadabra"))   # 5
print(get_count("hello world"))   # 3
print(get_count(""))              # 0
print(get_count("  "))            # 0