Write Django cmd for running lint (#100)

* Write Django cmd for running lint

* Respond to PR feedback

src/registrar/management/commands/lint.py

@@ -0,0 +1,63 @@
+from subprocess import run, CalledProcessError  # nosec
+
+from django.core.management.base import BaseCommand, CommandError
+
+
+class Command(BaseCommand):
+    """
+    Helper command for running installed linters.
+
+    Run using `./manage.py lint`.
+    """
+
+    help = "Runs linters: flake8 black mypy bandit"
+
+    # Add new linters here.
+    #
+    # To maintain security while using subprocess, avoid passing user input
+    # and, in all cases, make sure to use a list (not a string) for flags/args
+    # as this will quote the output.
+    linters = {
+        "flake8": {
+            "purpose": "Linting",
+            "args": ["flake8", ".", "--count", "--show-source", "--statistics"],
+        },
+        "black": {
+            "purpose": "Formatting",
+            "args": ["black", "--check", "."],
+        },
+        "mypy": {
+            "purpose": "Type checking",
+            "args": ["mypy", "."],
+        },
+        "bandit": {
+            "purpose": "Security scanning",
+            "args": ["bandit", "-r", "."],
+        },
+    }
+
+    def add_arguments(self, parser):
+        parser.add_argument("linters", nargs="*", type=str)
+
+    def handle(self, *args, **options):
+        try:
+            for linter in self.linters.values():
+                self.stdout.write(f"[manage.py lint] {linter['purpose']}. . .")
+                result = run(linter["args"])
+                if result.returncode:
+                    self.stderr.write(
+                        self.style.NOTICE(
+                            "[manage.py lint] Re-try with: [docker-compose exec app] "
+                            f"{' '.join(linter['args'])}"
+                        )
+                    )
+                    break
+                else:
+                    self.stdout.write(
+                        f"[manage.py lint] {linter['purpose']} completed with success!"
+                    )
+        except CalledProcessError as e:
+            raise CommandError(e)
+        self.stdout.write(
+            self.style.SUCCESS("[manage.py lint] All linters ran successfully.")
+        )