I create a git repository named `test_dir/` with git init,

in `test_dir`, I have some files and a subdirectory named code as below.

```
$ ls test_dir/
a.dat  b.dat  code/  c.py

$ ls test_dir/code/
e.dat  f.dat  test2.py  test3.py  test.py

```

I want to create a `.gitignore` file to ignore all files but not the python script file (`*.py`) in git root directory and in its subdirectory.

How should I configure my `.gitignore`?