add comment and use with

src/python/roms/__init__.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import base64
+import functools
 import hashlib
 import json
 import tarfile
@@ -10,10 +11,16 @@
 import requests
 
 
-def _download_roms():
-    """Downloads all roms in the form of a base64 file, then decodes it into a tar.gz, then extracts all the roms by matching it to the expected md5."""
+@functools.cache
+def _get_all_rom_hashes() -> dict[str, str]:
     # this is a map of {rom.bin : md5 checksum}
-    all_roms = json.load(open(Path(__file__).parent / "md5.json"))
+    with open(Path(__file__).parent / "md5.json") as f:
+        return json.load(f)
+
+
+def _download_roms() -> None:
+    """Downloads all roms in the form of a base64 file, then decodes it into a tar.gz, then extracts all the roms by matching it to the expected md5."""
+    all_roms = _get_all_rom_hashes()
 
     # use requests to download the base64 file
     url = "https://gist.githubusercontent.com/jjshoots/61b22aefce4456920ba99f2c36906eda/raw/00046ac3403768bfe45857610a3d333b8e35e026/Roms.tar.gz.b64"
@@ -51,9 +58,10 @@ def _download_roms():
         md5_hash = md5.hexdigest()
 
         # assert that the hash matches
-        assert (
-            md5_hash == all_roms[rom_name]
-        ), f"Rom {rom_name}'s hash does not match what was expected. Please report this to a dev."
+        assert md5_hash == all_roms[rom_name], (
+            f"Rom {rom_name}'s hash ({md5_hash}) does not match what was expected. "
+            "Please report this to a dev."
+        )
 
         # save this rom
         rom_path = Path(__file__).parent / rom_name
@@ -68,8 +76,8 @@ def get_rom_path(name: str) -> Path | None:
     bin_file = f"{name}.bin"
     bin_path = Path(__file__).parent / bin_file
 
-    # check if it exists within the md5.json
-    all_roms = json.load(open(Path(__file__).parent / "md5.json"))
+    # check if it exists within the the hash dictionary
+    all_roms = _get_all_rom_hashes()
     if bin_file not in all_roms:
         warnings.warn(f"Rom {name} not supported.")
         return None
@@ -89,5 +97,5 @@ def get_rom_path(name: str) -> Path | None:
 
 def get_all_rom_ids() -> list[str]:
     """Returns a list of all available rom_ids, ie: ['tetris', 'pong', 'zaxxon', ...]."""
-    all_roms = json.load(open(Path(__file__).parent / "md5.json"))
+    all_roms = _get_all_rom_hashes()
     return [key.split(".")[0] for key in all_roms.keys()]