<s>[INST] I'm writing a web app with the django framework. I've written a login function for users. How can I protect the input from SQL-Injections in the most efficient way? [/INST] Django has you covered here.
Never ever insert raw user input into your SQL queries. Always use query parameters, and Django makes this very easy:
User.objects.filter(username=username)  # Dangerous!

User.objects.filter(username=username)  # Safe, username is a parameter

So in your view:
User.objects.get(username=request.POST['username'])  # Dangerous
User.objects.get(username=request.POST.get('username'))  # Safe

Django will automatically escape the username and use it as a parameter in the SQL query, making it safe.
So in short: Always let Django construct the SQL query, and never insert raw user input. As long as you do that, you'll be safe from SQL injection.</s>\ <s>[INST] What is the difference between request.POST['username] and request.POST.get('username')? [/INST] They are quite similar, but there is one key difference:

request.POST['username'] will throw a KeyError if the username key is missing from the POST data.
request.POST.get('username') will simply return None if the key is missing, and won't throw an error.

So request.POST.get('username') is a safer choice if the username field is optional, or may be missing for some reason.
It's generally a good idea to use request.POST.get() to retrieve form data, to avoid potential KeyError exceptions being thrown.</s>\ <s>[INST] Is there any performance difference between these two methods? [/INST] 