Final a bit better.

.gitignore

@@ -1,2 +1 @@
 venv
-__pycache__

2021/day9.py

@@ -0,0 +1,13 @@
+import sys
+from collections import defaultdict
+from dataclasses import dataclass
+
+lines = sys.stdin.read().splitlines()
+
+# part 1
+answer_1 = ...
+print(f"answer 1 is {answer_1}")
+
+# part 2
+answer_2 = ...
+print(f"answer 2 is {answer_2}")