How to use Python sets and add strings to it in as a dictionary value

Question

I am trying to create a dictionary that has values as a Set object. I would like a collection of unique names associated with a unique reference). My aim is to try and create something like:

AIM:

Dictionary[key_1] = set('name')    
Dictionary[key_2] = set('name_2', 'name_3')

Adding to SET:

Dictionary[key_2].add('name_3')

However, using the set object breaks the name string into characters which is expected as shown here. I have tried to make the string a tuple i.e. set(('name')) and Dictionary[key].add(('name2')), but this does not work as required because the string gets split into characters.

Is the only way to add a string to a set via a list to stop it being broken into characters like

'n', 'a', 'm', 'e'

Any other ideas would be gratefully received.

Solution 1

You can write a single element tuple as @larsmans explained, but it is easy to forget the trailing comma. It may be less error prone if you just use lists as the parameters to the set constructor and methods:

Dictionary[key_1] = set(['name'])    
Dictionary[key_2] = set(['name_2', 'name_3'])

Dictionary[key_2].add(['name_3'])

should all work the way you expect.

Solution 2

('name') is not a tuple. It's just the expression 'name', parenthesized. A one-element tuple is written ('name',); a one-element list ['name'] is prettier and works too.

In Python 2.7, 3.x you can also write {'name'} to construct a set.

Comments

[12avi]

I find that when I use Dictionary.add['name_3'] after, I get an exception (unhashable type: 'list'). The only solution I found was therafter to use .add('name-3') --> Not now as a single list (but only for the Set constuctor).

[Duncan]

Please read what I wrote: .add(['name_3']) is not the same as .add['name_3']