Question: I have a dataframe like the below and want to remove trailing zeros in pairs of 2.

```
col1
99990000
11100000
22220000

```

```
data = {'col1': ['99990000', '11100000', '22220000']}
df = pd.DataFrame(data=data)

```

desired result

```
col1
9999
1110
2222

```

The below removes all trailing zeros not and not keeping 1110?

```
df['col1'].str.replace('00+$','')
df['col1'].str.rstrip('00')

```

Answer: 
Just to conceptualize the regex, here is an example. The solution from @mozway is much better but this focuses on the substitution only, ignoring pandas:

```
import re
col1 = [re.sub(r'(00)+$', '', num) for num in
              ['99990000', '11100000', '22220000']]
# ['9999', '1110', '2222']

```

* [`(00)+$`](https://regex101.com/r/1IVn5T/2)

[![enter image description here](https://i.stack.imgur.com/Yaf9r.png)](https://i.stack.imgur.com/Yaf9r.png)
Try this, it should work

```
df['col1'].str[:4]

```