Python - can a dict have a value that is a list?

Question

When using Python is it possible that a dict can have a value that is a list?

for example, a dictionary that would look like the following (see KeyName3's values):

{
keyName1 : value1,
keyName2: value2,
keyName3: {val1, val2, val3}
}

I already know that I can use 'defaultdict' however single values are (understandably) returned as a list.

The reason I ask is that my code must be generic so that the caller can retieve single key values as an item (just like from a dict key-value) and not as list (without having to specify pop[0] the list) - however also retrieve multiple values as a list.

If not then any suugestions would be welcome.

If someone can help then that would be great.

Thanks in Advance,

Paul

*I'm using Python 2.6 however writing scripts that must also be forward compatible with Python 3.0+.

Read here for details: http://docs.python.org/tutorial/datastructures.html#dictionaries and note if you new to python - tutorial is you the best friend — Artsiom Rudzenka, Jul 05 '11 at 20:03
For testing simple things like this, just use the interactive mode of python. You can experiment and find what is allowed and what is not. — tkerwin, Jul 05 '11 at 20:30

score 43 · Accepted Answer · answered Jul 05 '11 at 19:49

43

Yes. The values in a dict can be any kind of python object. The keys can be any hashable object (which does not allow a list, but does allow a tuple).

You need to use [], not {} to create a list:

{ keyName1 : value1, keyName2: value2, keyName3: [val1, val2, val3] }

answered Jul 05 '11 at 19:49

Wooble

87,717
12
108
131

The reason why one can use a tuple but not a list is because lists are mutable, so any calculation based on their "value" would not be idempotent (computing sense). – Marcin Feb 02 '12 at 16:25
@geoffspear, Cool but how to get value by keyname3 and list value 2? – Eswemenasja Sep 16 '17 at 16:14
1

@Eswemenasja yourdict["keyname3"][2] – Wooble Sep 16 '17 at 18:47
How do you unpack `keyName3` though? Such that `val1` `val2` `val3` will have `keyName3` in it? – jake wong Nov 13 '18 at 00:58

score 8 · Answer 2 · edited Apr 28 '12 at 17:28

8

Yes, it's possible:

d = {}
d["list key"] = [1,2,3]
print d

output:

{'list key': [1, 2, 3]}

edited Apr 28 '12 at 17:28

jamylak

128,818
30
231
230

answered Jul 05 '11 at 19:52

GreenMatt

18,244
7
53
79

score 0 · Answer 3 · answered Apr 28 '12 at 17:19

0

It definitely can have a list and any object as value but the dictionary cannot have a list as key because the list is mutable data structure and keys cannot be mutable else of what use are they.

answered Apr 28 '12 at 17:19

cobie

7,023
11
38
60

Python - can a dict have a value that is a list?

3 Answers3

Linked

Related