字典中的键错误。 如何使Python打印我的字典？

Question

In my homework, this question is asking me to make a function where Python should create dictionary of how many words that start with a certain letter in the long string is symmetrical. Symmetrical means the word starts with one letter and ends in the same letter. I do not need help with the algorithm for this. I definitely know I have it right, but however I just need to fix this Key error that I cannot figure out. I wrote d[word[0]] += 1 , which is to add 1 to the frequency of words that start with that particular letter.

The output should look like this (using the string I provided below): {'d': 1, 'i': 3, 't': 1}

t = '''The sun did not shine
it was too wet to play
so we sat in the house
all that cold cold wet day

I sat there with Sally
we sat there we two
and I said how I wish
we had something to do'''

def symmetry(text):
    from collections import defaultdict
    d = {}
    wordList = text.split()
    for word in wordList:
        if word[0] == word[-1]:
            d[word[0]] += 1
    print(d)
print(symmetry(t))

Answer 1

You never actually use collections.defaultdict , although you import it. Initialize d as defaultdict(int) , instead of as {} , and you're good to go.

def symmetry(text):
    from collections import defaultdict
    d = defaultdict(int)
    wordList = text.split()
    for word in wordList:
        if word[0] == word[-1]:
            d[word[0]] += 1
    print(d)

print(symmetry(t))

Results in:

defaultdict(<class 'int'>, {'I': 3, 't': 1, 'd': 1})

Answer 2

You're trying to increase the value of an entry which has yet to be made resulting in the KeyError . You could use get() for when there is no entry for a key yet; a default of 0 will be made ( or any other value you choose ). With this method, you would not need defaultdict ( although very useful in certain cases ).

def symmetry(text):
    d = {}
    wordList = text.split()
    for word in wordList:
        key = word[0]
        if key == word[-1]:
            d[key] = d.get(key, 0) + 1
    print(d)
print(symmetry(t))

Sample Output

{'I': 3, 'd': 1, 't': 1}