How do I repeat the values in one column multiple times based on the length of another column? Example: names = [Jack, Bob] and pets=[fish, cat, dog, bird]. I would like the dataframe to be:

```
    names   pets
0   Jack    fish
1   Jack    cat
2   Jack    dog
3   Jack    bird
4   Bob     fish
5   Bob     cat
6   Bob     dog
7   Bob     bird

```

How do I repeat the names (which will need to be filled in the names column) for every value in the pets column and then repeat the process for each name in names?