python codes for counting the occurrence of a letters in dictionary excluding digits

1def count_letters(text):
2      result = {}
3      # Go through each letter in the text
4      for letter in text:
5        # Check if the letter needs to be counted or not
6        if letter not in result:
7          result[letter.lower()] = 1
8        # Add or increment the value in the dictionary
9        else:
10          result[letter.lower()] += 1
11      return result
12
13    print(count_letters("AaBbCc"))
14    # Should be {'a': 2, 'b': 2, 'c': 2}
15
16    print(count_letters("Math is fun! 2+2=4"))
17    # Should be {'m': 1, 'a': 1, 't': 1, 'h': 1, 'i': 1, 's': 1, 'f': 1, 'u': 1, 'n': 1}
18
19    print(count_letters("This is a sentence."))
20    # Should be {'t': 2, 'h': 1, 'i': 2, 's': 3, 'a': 1, 'e': 3, 'n': 2, 'c': 1}
21