How to improve a for loop that will go through the values in my_dictionary as well as a list

Question

I am writing a for loop that will go through the values in my_dictionary as well as the values in the list. If a word from the list "words" is in the my_dictionary then append the list of values where the word was found once. The code below ran the code but the list look larger than I expected.

my_dictionary = {1: ['apple','dog','cat','bird'],
                 2: ['mouse','rat','elephant','donkey'],
                 3: ['tiger','lion','bear','tortoise']}

words = ['apple', 'dog', 'mouse', 'bear','tortoise']
                
def cen_lst(my_dict, words):
    new_lst = []
    for key, value in my_dict.items():
        for word in words:
            if word in value:
                new_lst.append(value)
    return new_lst  

output I expected:

['apple','dog','cat','bird', 'mouse','rat','elephant','donkey', 'tiger','lion','bear','tortoise' ]

Instead the output I am getting is:

[['apple', 'dog', 'cat', 'bird'],
 ['apple', 'dog', 'cat', 'bird'],
 ['mouse', 'rat', 'elephant', 'donkey'],
 ['tiger', 'lion', 'bear', 'tortoise'],
 ['tiger', 'lion', 'bear', 'tortoise']]

      

Answer 1

Every time it found a matching word it appends the entire list because of this line:

    new_lst.append(value)

The value for each iteration was the entire list at that key. That's why you got a list of lists. Simply replace value with word. This causes it to just append the matching word, not the list that the word is inside.

    new_list.append(word)

Answer 2

According to your description, you should use list.extend instead of list.append (you can refer to this for their differences), and do not extend every time the retrieval is successful:

>>> def cen_lst(my_dict, words):
...     new_lst = []
...     for value in my_dict.values():
...         if any(word in value for word in words):
...             new_lst.extend(value)
...     return new_lst
...
>>> cen_lst(my_dictionary, words)
['apple',
 'dog',
 'cat',
 'bird',
 'mouse',
 'rat',
 'elephant',
 'donkey',
 'tiger',
 'lion',
 'bear',
 'tortoise']