count the number of consonants in a string using python

"""Note that a non-vowel character is not always a consonant.So take care about other characters like numbers or special characters."""
vowels = 'aeiou'
s = input("Enter the string: ").lower()
count = 0
for i in range(len(s)):
    if s[i] not in vowels and s[i].isalpha(): #checks if character is alphabet
        count += 1

print(count)

#output : happy - 4