You have a couple of bugs here. Firstly, if I don't have a file named series.py, I get an error telling me so.
Secondly, if I _do_ have a file called dest, I get an error saying one can't be created. The way to handle this is through a try/except block. 
```try:
    os.mkdir(new_dest_)
except <AppropriateError>:
    #Do something else
```