updated package setup (#485)

* updated package setup

* updated to use python 3.9

* fixed test runner

* fixed typecheck tests

* fixed discrepencies

* added override to runner

* updated travis

* updated pre-commit hooks

* updated dep

scripts/git_helpers.py

@@ -0,0 +1,31 @@
+import shutil
+from typing import Optional
+
+from git import RemoteProgress, Repo
+
+from scripts.paths import DJANGO_SOURCE_DIRECTORY
+
+
+class ProgressPrinter(RemoteProgress):
+    def line_dropped(self, line: str) -> None:
+        print(line)
+
+    def update(self, op_code, cur_count, max_count=None, message=""):
+        print(self._cur_line)
+
+
+def checkout_django_branch(django_version: str, commit_sha: Optional[str]) -> Repo:
+    branch = f"stable/{django_version}.x"
+    if DJANGO_SOURCE_DIRECTORY.exists():
+        shutil.rmtree(DJANGO_SOURCE_DIRECTORY)
+    DJANGO_SOURCE_DIRECTORY.mkdir(exist_ok=True, parents=False)
+    repo = Repo.clone_from(
+        "https://github.com/django/django.git",
+        DJANGO_SOURCE_DIRECTORY,
+        progress=ProgressPrinter(),
+        branch=branch,
+        depth=100,
+    )
+    if commit_sha and repo.head.commit.hexsha != commit_sha:
+        repo.remote("origin").fetch(branch, progress=ProgressPrinter(), depth=100)
+        repo.git.checkout(commit_sha)