count frequent letters

def checkio(text):
    text = text.lower()
    check_list = sorted(set(text))
    store_no = 0
    store_letter = ''
    for letter in check_list:
        if letter.isalpha():
            ans = text.count(letter)
            if ans > store_no :
                store_letter = letter
                store_no = ans
                print(store_letter) 
    return store_letter

if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    assert checkio("Hello World!") == "l", "Hello test"
    assert checkio("How do you do?") == "o", "O is most wanted"
    assert checkio("One") == "e", "All letter only once."
    assert checkio("Oops!") == "o", "Don't forget about lower case."
    assert checkio("AAaooo!!!!") == "a", "Only letters."
    assert checkio("abe") == "a", "The First."
    print("Start the long test")
    assert checkio("a" * 9000 + "b" * 1000) == "a", "Long."
    print("The local tests are done.")

import string

def checkio(text):
"""
We iterate through latyn alphabet and count each letter in the text.
Then 'max' selects the most frequent letter.
For the case when we have several equal letter,
'max' selects the first from they.
"""
text = text.lower()
return max(string.ascii_lowercase, key=text.count)