Looping through Dictionary and add items to second dictionary

Python Help
1

I am trying to loop through a dictionary and add values that satisfy my true statemen to a second dictionary

At the moment, all I want to do is check and see if the value of each element is already a key in the entire dictionary and if so add it, otherwise go to next

mydict={“John” : “House”, “Eric” : “Turtle”, “Jimmy” : “John”, “Charles” : “Eric”}

myresult={“Jimmy” : “John”, “Charles” : Eric"} ← these two satisfy the true statement of the value being a key in the dictionary (i.e. value “John” is a key in “John”:“House”, etc.)

3

I’m pretty new and have no idea what the syntax should be… best i got is

mydict={‘John’ : ‘House’, ‘Eric’ : ‘Turtle’, ‘Jimmy’ : ‘John’, ‘Charles’ : ‘Eric’}
myresult={}
for x,y in mydict.items():
if y in mydict:
myresult.update({x,y})

which obviously doesn’t work otherwise i wouldn’t be posting here. This was copy and pasted from Jupytr so formatting may be off after submission

Screenshot_20220925_202338
Screenshot_20220925_2023381080×529 114 KB

5

You didn’t say in what way it “doesn’t work”, but the problem is that {x,y} is a set (note the comma), not dict. It’s {x: y} for a dict.

Additionally, when pasting a block code, enclose it in triple backticks:

```
…your code…
```

to make it look like this:

...your code...
6

Thanks Matthew, I just figured that out, however i think i need to expand on my example since I got that error to pass but the returned dict is blank.

words.txt is just a file of dictionary words, easy palindrome project here, I just want to add the reverse of the word as the value, then ask if the reverse word is one of the key’s already, then it is a legit palindrome (not some muddled garbage) …but when i call actual_palindroms it is blank

words = {line.strip().lower() for line in open('words.txt', 'r')}

def reverse(word):
    return str(''.join(reversed(word)))

all_palindromes = {}
actual_palindromes={}

for word in words:
    all_palindromes[word]=str([reverse(word)])

for x,y in all_palindromes.items():
    if y in all_palindromes:
        actual_palindromes.update({x:y})

i’m “guessing” it may have something to do with the join, it looks like after i join the reverse it is a string and a set? e.g. ‘john’ : “[‘nhoj’]” but maybe i’m wrong, again i’m still pretty new

7

You wrote str([reverse(word)]), which will reverse the word, put it into a list (note the [...] there), and then convert that into a string.

Incidentally, .join returns a string, so you don’t need to use str(...) on the result. An even shorter method to reverse a string is to use slicing: word[ : : -1].

8

Can you describe this project? At first glance and without description of terms, conditions and algorithm it seems rather complicated way to determine whether word is palindrome or not.

9

Hi Charles,

You seem to be over-complicating your palindrome project.

A word is a palindrome if it is the same forwards and backwards. So all you need to do is start with a list of words, and check each word:

words = {line.strip().lower() for line in open('words.txt', 'r')}

palindromes = set()

for word in words:
    if word == word[::-1]:
        print(word, 'is a palindrome')
        palindromes.add(word)

Related to palindromes are words which form a different word when reversed. The most common word for those is, apparently (s)emordnilap. We can check for them as well:

words = {line.strip().lower() for line in open('words.txt', 'r')}

palindromes = set()
emordnilaps = set()

for word in words:
    backwards = word[::-1]
    if word == backwards:
        print(word, 'is a palindrome')
        palindromes.add(word)
    elif backwards in words:
        print(word, 'is an emordnilap')
        emordnilaps.add(word)

There’s no need for a dict in this.

2 Likes
10

I think you’re right :joy: I suppose I shouldn’t have dove into python after working for 12 hours but what you said makes sense, if it is same word is same forwards and backwards i’m all good; i got hung up on needing the reverse and went down a long unneeded rabbit hole