fix presubmit

Author: shuoweil

bigframes/display/anywidget.py

@@ -75,15 +75,16 @@ def __init__(self, dataframe: bigframes.dataframe.DataFrame):
         # Initialize data fetching attributes.
         self._batches = dataframe.to_pandas_batches(page_size=initial_page_size)
 
-        # 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)
 
+        # set traitlets properties that trigger observers
+        self.page_size = initial_page_size
+        self._reset_batches_for_new_page_size()
+
         # get the initial page
         self._set_table_html()
 
@@ -187,19 +188,21 @@ def _reset_batches_for_new_page_size(self):
 
     def _set_table_html(self):
         """Sets the current html data based on the current page and page size."""
-        start = self.page * self.page_size
-        end = start + self.page_size
-
-        # fetch more data if the requested page is outside our cache
-        cached_data = self._cached_data
-        while len(cached_data) < end and not self._all_data_loaded:
-            if self._get_next_batch():
-                cached_data = self._cached_data
-            else:
-                break
-
-        # Get the data for the current page
-        page_data = cached_data.iloc[start:end]
+        # For empty dataframe, render empty table with headers.
+        if self.row_count == 0:
+            page_data = self._cached_data
+        else:
+            start = self.page * self.page_size
+            end = start + self.page_size
+
+            # fetch more data if the requested page is outside our cache
+            cached_data = self._cached_data
+            while len(cached_data) < end and not self._all_data_loaded:
+                if self._get_next_batch():
+                    cached_data = self._cached_data
+                else:
+                    break
+            page_data = cached_data.iloc[start:end]
 
         # Generate HTML table
         self.table_html = bigframes.display.html.render_html(
@@ -218,8 +221,5 @@ def _page_size_changed(self, _change: Dict[str, Any]):
         # Reset the page to 0 when page size changes to avoid invalid page states
         self.page = 0
 
-        # Reset batches to use new page size for future data fetching
-        self._reset_batches_for_new_page_size()
-
         # Update the table display
         self._set_table_html()