I have the following pandas data frame:

```
import pandas as pd
df = pd.DataFrame({ 'gene':["1 // foo // blabla",
                                   "2 // bar // lalala",
                                   "3 // qux // trilil",
                                   "4 // woz // hohoho"], 'cell1':[5,9,1,7], 'cell2':[12,90,13,87]})
df = source_df[["gene","cell1","cell2"]]

```

It looks like this:

```
                 gene  cell1  cell2
0  1 // foo // blabla      5     12
1  2 // bar // lalala      9     90
2  3 // qux // trilil      1     13
3  4 // woz // hohoho      7     87

```

What I want to get is this:

```
   gene    cell1  cell2
0   foo       5     12
1   bar       9     90
2   qux       1     13
3   woz       7     87

```

Namely select 2nd element of the splited string by `//` as delimiter.

The best I can do is this:

```
df["gene"] = df["gene"].str.split(" // ")
df
Out[17]:
               gene  cell1  cell2
0  [1, foo, blabla]      5     12
1  [2, bar, lalala]      9     90
2  [3, qux, trilil]      1     13
3  [4, woz, hohoho]      7     87

```

What's the right way to do it?