How to use sadd with multiple elements in Redis using Python API?

Question

Please consider the following example

>>import redis
>>redis_db_url = '127.0.0.1'
>>r = redis.StrictRedis(host = redis_db_url,port = 6379,db = 0)
>>r.sadd('a',1)
>>r.sadd('a',2)
>>r.sadd('a',3)
>>r.smembers('a')

[+] output: set(['1', '3', '2'])

>>r.sadd('a',set([3,4]))
>>r.smembers('a')

[+] output: set(['1', '3', '2', 'set([3, 4])'])

 >>r.sadd('a',[3,4])
 >>r.smember('a')

[+] set(['1', '[3, 4]', '3', '2', 'set([3, 4])'])

According to the official documentation in https://redis-py.readthedocs.org/en/latest/ sadd(name, *values) Add value(s) to set name

So is it a bug or I am missing something ?

Solution 1

When you see the syntax *values in an argument list, it means the function takes a variable number of arguments.

Therefore, call it as

r.sadd('a', 1, 2, 3)

You can pass an iterable by using the splat operator to unpack it:

r.sadd('a', *set([3, 4]))

or

r.sadd('a', *[3, 4])

Solution 2

Consider the following:

r.sadd('a', 1, 2, 3)

That should do the trick.

Comments

[Seaux]

I could be wrong, but i don't think you have to cast as a set before unpacking

[nneonneo]

No, you don't, but I was following the example in the author's question. In this case the inline syntax is just a shortcut for indicating that you can do this with an arbitrary set (or indeed, an arbitrary iterable).

[nneonneo]

And really, on any recent Python you can just do *{3, 4} which is the native syntax for set literals, eliminating the "cast" altogether.

[Seaux]

Agreed. I just wanted to clarify the point because I didn't want readers to think you had to cast to set for use in sadd or something. I'd recommend editing the answer to separate out the declaration of the iterable (set) in another line or just remove the casting all together.