To add to what Carles Barrobés said, you can generate a new key using the method that Django uses in startproject:
from django.utils.crypto import get_random_string
chars="abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*(-_=+)"
get_random_string(50, chars)
For Django 1.10 and above, the above code snippet is nicely wrapped up in a function.
from django.core.management.utils import get_random_secret_key
get_random_secret_key()
Link to GitHub repo