Count the character frequency

Count the number of characters (character frequency) in a string.
Sample String :
google.com
Expected Result :
{‘o’: 3, ‘g’: 2, ‘.’: 1, ‘e’: 1, ‘l’: 1, ‘m’: 1, ‘c’: 1}
def char_frequency(S):
    D = {}
    for chr in S:
        if chr in D.keys():
            D[chr] += 1
        else:
            D[chr] = 1
    return D

# test
print(char_frequency('google.com'))

Output:

{'o': 3, '.': 1, 'g': 2, 'l': 1, 'e': 1, 'c': 1, 'm': 1}