make textstat optional in the flyte callback handler (#7186)

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This PR makes the `textstat` library optional in the Flyte callback
handler.

@hinthornw, would you mind reviewing this PR since you merged the flyte
callback handler code previously?

---------

Signed-off-by: Samhita Alla <aallasamhita@gmail.com>

langchain/callbacks/flyte_callback.py

@@ -39,6 +39,7 @@ def import_flytekit() -> Tuple[flytekit, renderer]:
 def analyze_text(
     text: str,
     nlp: Any = None,
+    textstat: Any = None,
 ) -> dict:
     """Analyze text using textstat and spacy.
 
@@ -51,7 +52,7 @@ def analyze_text(
             files serialized to HTML string.
     """
     resp: Dict[str, Any] = {}
-    textstat = import_textstat()
+    if textstat is not None:
         text_complexity_metrics = {
             "flesch_reading_ease": textstat.flesch_reading_ease(text),
             "flesch_kincaid_grade": textstat.flesch_kincaid_grade(text),
@@ -78,16 +79,13 @@ def analyze_text(
         dep_out = spacy.displacy.render(  # type: ignore
             doc, style="dep", jupyter=False, page=True
         )
-
         ent_out = spacy.displacy.render(  # type: ignore
             doc, style="ent", jupyter=False, page=True
         )
-
         text_visualizations = {
             "dependency_tree": dep_out,
             "entities": ent_out,
         }
-
         resp.update(text_visualizations)
 
     return resp
@@ -98,10 +96,19 @@ class FlyteCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
 
     def __init__(self) -> None:
         """Initialize callback handler."""
-        import_textstat()  # Raise error since it is required
         flytekit, renderer = import_flytekit()
         self.pandas = import_pandas()
 
+        self.textstat = None
+        try:
+            self.textstat = import_textstat()
+        except ImportError:
+            logger.warning(
+                "Textstat library is not installed. \
+                It may result in the inability to log \
+                certain metrics that can be captured with Textstat."
+            )
+
         spacy = None
         try:
             spacy = import_spacy()
@@ -123,7 +130,7 @@ class FlyteCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
                     "FlyteCallbackHandler uses spacy's en_core_web_sm model"
                     " for certain metrics. To download,"
                     " run the following command in your terminal:"
-                    " `python -m spacy download en_core_web_sm` command."
+                    " `python -m spacy download en_core_web_sm`"
                 )
 
         self.table_renderer = renderer.TableRenderer
@@ -180,11 +187,10 @@ class FlyteCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
             for generation in generations:
                 generation_resp = deepcopy(resp)
                 generation_resp.update(flatten_dict(generation.dict()))
-                if self.nlp:
+                if self.nlp or self.textstat:
                     generation_resp.update(
                         analyze_text(
-                            generation.text,
+                            generation.text, nlp=self.nlp, textstat=self.textstat
-                            nlp=self.nlp,
                         )
                     )