remove expensive len() call

Author: shuoweil

bigframes/display/anywidget.py

@@ -44,8 +44,10 @@
 
 
 class TableWidget(WIDGET_BASE):
-    """
-    An interactive, paginated table widget for BigFrames DataFrames.
+    """An interactive, paginated table widget for BigFrames DataFrames.
+
+    This widget provides a user-friendly way to display and navigate through
+    large BigQuery DataFrames within a Jupyter environment.
     """
 
     def __init__(self, dataframe: bigframes.dataframe.DataFrame):
@@ -74,15 +76,18 @@ def __init__(self, dataframe: bigframes.dataframe.DataFrame):
         # Initialize data fetching attributes.
         self._batches = dataframe.to_pandas_batches(page_size=initial_page_size)
 
+        # Access total_rows through type casting (internal use only)
+        from bigframes.core.blocks import PandasBatches
+
+        if isinstance(self._batches, PandasBatches):
+            self.row_count = self._batches.total_rows or 0
+        else:
+            # Fallback for compatibility
+            self.row_count = 0
+
         # set traitlets properties that trigger observers
         self.page_size = initial_page_size
 
-        # len(dataframe) is expensive, since it will trigger a
-        # SELECT COUNT(*) query. It is a must have however.
-        # TODO(b/428238610): Start iterating over the result of `to_pandas_batches()`
-        # before we get here so that the count might already be cached.
-        self.row_count = len(dataframe)
-
         # get the initial page
         self._set_table_html()