Make bs4 a local import in recursive_url_loader.py (langchain-ai#6693)

Resolve langchain-ai#6679

langchain/document_loaders/recursive_url_loader.py

@@ -2,7 +2,6 @@
 from urllib.parse import urlparse
 
 import requests
-from bs4 import BeautifulSoup
 
 from langchain.docstore.document import Document
 from langchain.document_loaders.base import BaseLoader
@@ -21,6 +20,13 @@ def get_child_links_recursive(
     ) -> Set[str]:
         """Recursively get all child links starting with the path of the input URL."""
 
+        try:
+            from bs4 import BeautifulSoup
+        except ImportError:
+            raise ImportError(
+                "The BeautifulSoup package is required for the RecusiveUrlLoader."
+            )
+
         # Construct the base and parent URLs
         parsed_url = urlparse(url)
         base_url = f"{parsed_url.scheme}://{parsed_url.netloc}"