I have data stored in the data frame. Now I want to filter out the data within specific columns using Keywords.
For Example:
let my dataframe be:

```
    customer    product         state
0   shyam       pen drive       delhi
1   suresh      hard disk       punjab
2   shanu       USB pen drive   haryana
3   rohan       pen drive 16gb  uttarpradesh

```

Now I want to filter this dataframe in column 'product' with values containing 'pen' only.
so the result should look like:

```
    customer    product         state
0   shyam       pen drive       delhi
2   shanu       USB pen drive   haryana
3   rohan       pen drive 16gb  uttarpradesh

```

Every suggestion would be appreciated.