Handle empty dataframes without crashing

Author: kdkavanagh

src/dt_browser/browser.py

@@ -245,7 +245,7 @@ def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.border_title = "Row Detail"
         self._dt = CustomTable(
-            pl.DataFrame(),
+            pl.DataFrame({"Temp": []}),
             pl.DataFrame().with_row_index(name=INDEX_COL).select([INDEX_COL]),
             cursor_type=CustomTable.CursorType.NONE,
         )
@@ -461,7 +461,7 @@ async def watch_show_row_detail(self):
         if not self.show_row_detail:
             if existing := self.query(RowDetail):
                 existing.remove()
-        else:
+        elif not self._display_dt.is_empty():
             await self.query_one("#main_hori", Horizontal).mount(self._row_detail)
 
     async def action_show_bookmarks(self):
@@ -492,6 +492,8 @@ def _set_active_dt(self, active_dt: pl.DataFrame, new_row: int | None = None):
 
         self._display_dt = active_dt
         self.cur_total_rows = len(self._display_dt)
+        if self._display_dt.is_empty():
+            self.show_row_detail = False
         self.watch_active_search(goto=False)
         (table := self.query_one("#main_table", CustomTable)).set_dt(self._display_dt, self._meta_dt)
         if new_row is not None:
@@ -529,9 +531,7 @@ async def watch_timestamp_columns(self):
                     ).alias(self._ts_col_names[x])
                     for x in self.timestamp_columns
                 ]
-                print(calc_expr)
                 self._original_dt = self._original_dt.with_columns(calc_expr)
-                print(self._original_dt.columns)
             except Exception as e:
                 self.notify(f"Failed to compute timestamp columns: {e}", severity="warn", timeout=5)
             finally:
@@ -614,18 +614,20 @@ def check_action(self, action: str, parameters: tuple[object, ...]) -> bool | No
         if not edtq.has_focus and action in (x.action if isinstance(x, Binding) else x[1] for x in DtBrowser.BINDINGS):
             return False
 
-        if action == "iter_search":
-            if not self.active_search_queue:
-                return False
-            if bool(parameters[0]) and self.active_search_idx == len(self.active_search_queue) - 1:
-                return False
-            if not bool(parameters[0]) and self.active_search_idx == 0:
-                return False
-        if action == "show_bookmarks":
-            return self._bookmarks.has_bookmarks
-
-        if action == "timestamp_selector":
-            return len(self._ts_cols) > 0
+        match action:
+            case "iter_search":
+                if not self.active_search_queue:
+                    return False
+                if bool(parameters[0]) and self.active_search_idx == len(self.active_search_queue) - 1:
+                    return False
+                if not bool(parameters[0]) and self.active_search_idx == 0:
+                    return False
+            case "show_bookmarks":
+                return self._bookmarks.has_bookmarks
+            case "timestamp_selector":
+                return len(self._ts_cols) > 0
+            case "toggle_row_detail":
+                return not self._display_dt.is_empty()
 
         return True
 

src/dt_browser/custom_table.py

@@ -229,14 +229,17 @@ def _build_header_contents(self):
         )
 
         _, header_width = self._build_base_header(self._dt.columns)
-        self.virtual_size = Size(header_width, len(self._dt) + HEADER_HEIGHT)
+        # Max to handle empty dataframe message
+        self.virtual_size = Size(header_width, max(1, len(self._dt)) + HEADER_HEIGHT)
 
     def set_metadata(self, metadata_dt: pl.DataFrame):
         self._metadata_dt = metadata_dt
         self._render_header_and_table = None
         self.refresh(repaint=True)
 
     def set_dt(self, dt: pl.DataFrame, metadata_dt: pl.DataFrame):
+        if not dt.columns:
+            raise Exception("Cannot display a datatable with no columns")
         self._dt = dt
         self._metadata_dt = metadata_dt
         self._widths = {x: max(len(x), self._measure(self._dt[x])) for x in self._dt.columns}
@@ -577,7 +580,17 @@ def render_lines(self, crop: Region):
 
         self._lines.clear()
         self._lines.append(cur_header)
-        if not render_df.is_empty():
+        if render_df.is_empty():
+            msg = "< Empty Dataframe >"
+            padding = int((self.scrollable_content_region.width - len(msg)) / 2)
+            msg = f"{' '*padding}{msg}{' '*padding}"
+            self._lines.append(
+                Strip(
+                    [Segment(msg)],
+                    cell_length=self.scrollable_content_region.width,
+                )
+            )
+        else:
             rend = render_df.lazy()
             if self._cursor_type == CustomTable.CursorType.NONE:
                 rend = rend.select(
@@ -684,6 +697,8 @@ def _measure(self, arr: pl.Series) -> int:
         if dtype.is_(pld.Boolean()):
             return 7
 
+        if arr.is_empty():
+            return 0
         # for everything else, we need to compute it
         width = arr.cast(pl.Utf8(), strict=False).fill_null("<null>").str.len_chars().max()
         assert isinstance(width, int)