How to iteratively append key-value pairs to a dictionary in Python?

Question

I have the following code:

list1 = ['a', 'b', 'c']
dict1 = {}

for item in list1:
   dict1.update({"letter": item})

print(dict1)

I want to iterate over the list and add each element into the dictionary with the same key for each element. So in this case, the required output should be:

{'letter': 'a', 'letter': 'b', 'letter': 'c'}

But the output I get is:

{'letter': 'c'}

Only the last element is added to the dict. How can I get the required output?

Thanks in advance.

you sure you dont want `{'a':'letter','b':'letter','c':'letter'}` ? since that is possible ... — Joran Beasley, Jul 09 '15 at 19:16
If you want multiple items per key, give each key a list of values rather than an atomic value. — Jacques de Hooge, Jul 09 '15 at 19:16
What about a list of unique dictionaries, like so: [{"letter": "a"}, {"letter": "b"}, {"letter": "c"}] @vignesh Kalai — modarwish, Jul 09 '15 at 19:17
I am working on implementing the NB classifier using NLTK like [here](http://www.nltk.org/howto/classify.html). The features are taken as a list of tuples; within each tuple, there is a dictionary and a string to represent the class label.The dictionaries seem to have the same keys.. @TigerhawkT3 — modarwish, Jul 09 '15 at 19:22
http://stackoverflow.com/questions/960733/python-creating-a-dictionary-of-lists — Constantin, Jul 09 '15 at 19:23
You might want to use the dictionary initiated list. Then the key will store a list of values. You can use defaultdict from collections. — sweet_sugar, Jul 09 '15 at 19:34

The6thSense · Accepted Answer · 2015-07-09T19:29:36.657

0

sa=[{"letter":a} for in list1]
sa
[{"letter":a},{"letter":b},{"letter":c}]

But there is no need to do this though

The right method would be to add a list to the key letter

dict1={"letter":[]}
dict1["letter"].extend([a for a in list1])
dict
{"letter":["a","b","c"]}

edited Jul 09 '15 at 19:29

answered Jul 09 '15 at 19:21

The6thSense

8,103
8
31
65

This is almost certainly solving [Problem Y](http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem). – TigerhawkT3 Jul 09 '15 at 19:21
What's the benefit of showing the output of an unnecessary operation? – TigerhawkT3 Jul 09 '15 at 19:25
I don't understand how it's an answer in the slightest, but it looks like you've helped someone solve his [Problem Y](http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem), so whatever. – TigerhawkT3 Jul 09 '15 at 19:31
Thanks for the help. Experimentation is never wrong. @Vignesh Kalai – modarwish Jul 09 '15 at 19:35

How to iteratively append key-value pairs to a dictionary in Python?

1 Answers1