beginner python user here

I read a logfile with IP adresses and timestamps and want to create a list with each IP showing at what instant the IP was seen.
So one IP can have multiple timestamps.
I think a dictionary of sets would do the job, but I cannot figure out how to create this dynamically. 

example data

```
10.1.1.10 1441110489
10.1.1.15 1441110490
10.1.1.10 1441110491
10.1.1.11 1441110492
10.1.1.10 1441110492
10.1.1.11 1441110493

```

should result in

```
10.1.1.10 1441110489,1441110491,1441110492
10.1.1.11 1441110492,1441110493
10.1.1.15 1441110490

```

this part is self-answered below.

Bonus problem: later I want to search in this data for a timestamp but with a little time window. So not an exact match. I guess I need to iterate over all the data for my search? (I can post this as a separate question)