I have this sample data in a cell:

```
EmployeeID

2016-CT-1028
2016-CT-1028
2017-CT-1063
2017-CT-1063
2015-CT-948
2015-CT-948

```

So, my problem is how can I add `0` inside this data `2015-CT-948` to 
make it like this `2015-CT-0948`.
I tried this code:

```
pattern = re.compile(r'(\d\d+)-(\w\w)-(\d\d\d)')
newlist = list(filter(pattern.match, idList))

```

Just to get the match regex pattern then add the `0` with `zfill()` but its not working. Please, can someone give me an idea on how can I do it. Is there anyway I can do it in regex or in pandas. Thank you!