[Python] 'method' object is not subscriptable error appears when using get function

Django rises an error of ('method' object is not subscriptable) when trying to access username attribute from class User . imports :

from django.shortcuts import render
from .models import Post
from django.contrib.auth.models import User
from django.views.generic import ListView, DetailView, CreateView, UpdateView, DeleteView
from django.contrib.auth.mixins import LoginRequiredMixin, UserPassesTestMixin
from django.shortcuts import get_object_or_404


the function that cause the error :

class UserPostListView(PostListView):
model = Post
fields = ['title', 'content']
context_object_name = 'posts'
paginate_by = 2
def get_queryset(self):
user = get_object_or_404(User, username= self.kwargs.get('username'))
return Post.objects.filter(author=user).order_by['-date']


I tried using square brackets instead of parentheses, but it raised a similar error .

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