retyped day2, completed days 3 and 4, modified template

day3/part2.py

@@ -0,0 +1,38 @@
+from string import ascii_lowercase
+
+
+def parse(filename: str) -> list[tuple[str, str, str]]:
+    groups = []
+    i = 0
+    group = []
+    with open(filename) as f:
+        for line in f.readlines():
+            if i % 3 == 0 and i != 0:
+                groups.append(group)
+                group = []
+            group.append(line[:-1])
+            i += 1
+        groups.append(group)
+    return tuple(groups)
+
+
+def convert(char: str) -> int:
+    return ord(char) - 96 if char in ascii_lowercase else ord(char) - 38
+
+
+def common_character(group: tuple[str, str, str]) -> str:
+    assert len(group) == 3
+    b1, b2, b3 = group
+    return filter(lambda c: c in b2 and c in b3, b1).__next__()
+
+
+def solve(groups: list[tuple[str, str, str]]) -> int:
+    return sum(map(convert, map(common_character, groups)))
+
+
+def main():
+    print(solve(parse("input")))
+
+
+if __name__ == "__main__":
+    main()