Question: I'd like to know how could I find all files whose extension can be `.xml` and `.py` that contain the string "Jason" under a path "./" recursively?

Or how could I exclude `.po` from the search?

Answer: 
Try the following command. It will search only in the `.xml` and `.py` files for your name:

```
find . -type f \( -iname \*.xml -o -iname \*.py \) | xargs grep "Jason"

```

Hope this helps!
How I understand from your question above, u need to show all files with "Jason" string into. So, may be this can help you:

```
find . -type f \( -name "*.xml" -o -name "*.py" \) | grep -r "Jason" | cut -d':' -f1 | uniq

```