From 3635d96a0375670af9ffafd7e42d4ffce1c81149 Mon Sep 17 00:00:00 2001
From: Michael Bianco <iloveitaly@gmail.com>
Date: Sat, 8 Jul 2023 18:34:29 -0600
Subject: [PATCH] refactor: only fallback to approximate if tiktoken fails
 (#1898)

---
 langchain/src/base_language/count_tokens.ts | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/langchain/src/base_language/count_tokens.ts b/langchain/src/base_language/count_tokens.ts
index 80be94b0fed9..863c0297d564 100644
--- a/langchain/src/base_language/count_tokens.ts
+++ b/langchain/src/base_language/count_tokens.ts
@@ -68,8 +68,7 @@ export const calculateMaxTokens = async ({
   prompt,
   modelName,
 }: CalculateMaxTokenProps) => {
-  // fallback to approximate calculation if tiktoken is not available
-  let numTokens = Math.ceil(prompt.length / 4);
+  let numTokens;
 
   try {
     numTokens = (await encodingForModel(modelName)).encode(prompt).length;
@@ -77,6 +76,9 @@ export const calculateMaxTokens = async ({
     console.warn(
       "Failed to calculate number of tokens, falling back to approximate count"
     );
+
+    // fallback to approximate calculation if tiktoken is not available
+    numTokens = Math.ceil(prompt.length / 4);
   }
 
   const maxTokens = getModelContextSize(modelName);