fix(tokens): incorrect caching of async tokenizer (#47)

The async tokenizer would crash if it was called multiple times in the same process

examples/tokens.py

@@ -1,12 +1,32 @@
 #!/usr/bin/env poetry run python
 
-from anthropic import Anthropic
+import asyncio
 
-client = Anthropic()
+from anthropic import Anthropic, AsyncAnthropic
 
-text = "hello world!"
 
-tokens = client.count_tokens(text)
-print(f"'{text}' is {tokens} tokens")
+def sync_tokens() -> None:
+    client = Anthropic()
 
-assert tokens == 3
+    text = "hello world!"
+
+    tokens = client.count_tokens(text)
+    print(f"'{text}' is {tokens} tokens")
+
+    assert tokens == 3
+
+
+async def async_tokens() -> None:
+    anthropic = AsyncAnthropic()
+
+    text = "fist message"
+    tokens = await anthropic.count_tokens(text)
+    print(f"'{text}' is {tokens} tokens")
+
+    text = "second message"
+    tokens = await anthropic.count_tokens(text)
+    print(f"'{text}' is {tokens} tokens")
+
+
+sync_tokens()
+asyncio.run(async_tokens())

src/anthropic/_tokenizers.py

@@ -1,5 +1,7 @@
+from __future__ import annotations
+
+from typing import cast
 from pathlib import Path
-from functools import lru_cache
 
 from anyio import Path as AsyncPath
 
@@ -13,15 +15,29 @@ def _get_tokenizer_cache_path() -> Path:
     return Path(__file__).parent / "tokenizer.json"
 
 
-@lru_cache(maxsize=None)
+_tokenizer: Tokenizer | None = None
+
+
+def _load_tokenizer(raw: str) -> Tokenizer:
+    global _tokenizer
+
+    _tokenizer = cast(Tokenizer, Tokenizer.from_str(raw))
+    return _tokenizer
+
+
 def sync_get_tokenizer() -> Tokenizer:
+    if _tokenizer is not None:
+        return _tokenizer
+
     tokenizer_path = _get_tokenizer_cache_path()
     text = tokenizer_path.read_text()
-    return Tokenizer.from_str(text)
+    return _load_tokenizer(text)
 
 
-@lru_cache(maxsize=None)
 async def async_get_tokenizer() -> Tokenizer:
+    if _tokenizer is not None:
+        return _tokenizer
+
     tokenizer_path = AsyncPath(_get_tokenizer_cache_path())
     text = await tokenizer_path.read_text()
-    return Tokenizer.from_str(text)
+    return _load_tokenizer(text)