changed ValueError to ImportError (#5006)

# changed ValueError to ImportError in except

Several places with this bug. ValueError does not catch ImportError.

langchain/docstore/wikipedia.py

@@ -15,7 +15,7 @@ class Wikipedia(Docstore):
         try:
             import wikipedia  # noqa: F401
         except ImportError:
-            raise ValueError(
+            raise ImportError(
                 "Could not import wikipedia python package. "
                 "Please install it with `pip install wikipedia`."
             )

langchain/utilities/arxiv.py

@@ -58,7 +58,7 @@ class ArxivAPIWrapper(BaseModel):
             )
             values["arxiv_result"] = arxiv.Result
         except ImportError:
-            raise ValueError(
+            raise ImportError(
                 "Could not import arxiv python package. "
                 "Please install it with `pip install arxiv`."
             )

langchain/utilities/wikipedia.py

@@ -41,7 +41,7 @@ class WikipediaAPIWrapper(BaseModel):
             wikipedia.set_lang(values["lang"])
             values["wiki_client"] = wikipedia
         except ImportError:
-            raise ValueError(
+            raise ImportError(
                 "Could not import wikipedia python package. "
                 "Please install it with `pip install wikipedia`."
             )