Count Letters

This function in Python, uses a dictionary to count the frequency of letters in the input string.

Only letters should be counted, not blank spaces, numbers, or punctuation.

Upper case should be considered the same as lower case.

def count_letters(text):
    result = {}
    # Go through each letter in the text
    for letter in text:
        letter = letter.lower()
        # Check if the letter needs to be counted or not
        if letter.isalpha():
            # Add or increment the value in the dictionary
            if letter not in result:
                result[letter] = 0
                #print("Adding " + letter + " to dictionary")  
            result[letter] +=1  
    
    return result

print(count_letters("AaBbCc"))
# Should be {'a': 2, 'b': 2, 'c': 2}

print(count_letters("Math is fun! 2+2=4"))
# Should be {'m': 1, 'a': 1, 't': 1, 'h': 1, 'i': 1, 's': 1, 'f': 1, 'u': 1, 'n': 1}

print(count_letters("This is a sentence."))
# Should be {'t': 2, 'h': 1, 'i': 2, 's': 3, 'a': 1, 'e': 3, 'n': 2, 'c': 1}