I have column in a dataframe and i am trying to extract 8 digits from a string. How can I do it

```
    Input
 Shipment ID
20180504-S-20000
20180514-S-20537
20180514-S-20541
20180514-S-20644
20180514-S-20644
20180516-S-20009
20180516-S-20009
20180516-S-20009
20180516-S-20009

```

**Expected Output**

```
Order_Date
20180504
20180514
20180514
20180514
20180514
20180516
20180516
20180516
20180516

```

I tried below code and it didnt work.

```
data['Order_Date'] = data['Shipment ID'][:8]

```