Looking for a sort of chain method to apply to a df.

consider the following DF.

```
Store
1
33
455

```

what I'm trying to do is ascertain the length and append a 0 based on the length.

I've tried a simple for loop which i thought may work

```
for s in df.Store:
  if s.str.len() == 3:
    "0" + s

```

however this doesn't work.

I've also tried slicing the DF and each variable one by one

```
if df.Store == df[df['Store'].str.len() == 1]:
    "0" + df.Store

```

but neither work and just return a blank output.

I'm working with an object dtype.

desired output:

```
Store
0001
0033
0455

```