add the SpellingBee task so that nanochat can count r in strawberry etc. along the way we had to add a bunch of new functionality, e.g. extend the calculator to support the count function of python. possibly the current TaskMixture uses way too many synthetic examples of SpellingBee because the eval gives us exactly 100% performance on spelling. We can tune this later to reclaim some wall clock time here I think

nanochat/common.py

@@ -5,6 +5,8 @@ Common utilities for nanochat.
 import os
 import re
 import logging
+import fcntl
+import urllib.request
 import torch
 import torch.distributed as dist
 
@@ -56,6 +58,44 @@ def get_base_dir():
     os.makedirs(nanochat_dir, exist_ok=True)
     return nanochat_dir
 
+def download_file_with_lock(url, filename):
+    """
+    Downloads a file from a URL to a local path in the base directory.
+    Uses a lock file to prevent concurrent downloads among multiple ranks.
+    """
+    base_dir = get_base_dir()
+    file_path = os.path.join(base_dir, filename)
+    lock_path = file_path + ".lock"
+
+    if os.path.exists(file_path):
+        return file_path
+
+    with open(lock_path, 'w') as lock_file:
+
+        # Only a single rank can acquire this lock
+        # All other ranks block until it is released
+        fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX)
+
+        if os.path.exists(file_path):
+            return file_path
+
+        print(f"Downloading {url}...")
+        with urllib.request.urlopen(url) as response:
+            content = response.read().decode('utf-8')
+
+        with open(file_path, 'w') as f:
+            f.write(content)
+
+        print(f"Downloaded to {file_path}")
+
+    # Clean up the lock file after the lock is released
+    try:
+        os.remove(lock_path)
+    except OSError:
+        pass  # Ignore if already removed by another process
+
+    return file_path
+
 def print0(s="",**kwargs):
     ddp_rank = int(os.environ.get('RANK', 0))
     if ddp_rank == 0: