tabular: document sheet data structure, log sizes

 * Add more documentation for the `sheets` data structure.  Rename or
   create some derived variables to make code clearer.

 * Log the number of columns and rows when one or the other exceeds
   the maximum allowed number.

Author: felliott

mfr/extensions/tabular/exceptions.py

@@ -29,9 +29,14 @@ class TableTooBigError(TabularRendererError):
 
     __TYPE = 'tabular_table_too_big'
 
-    def __init__(self, message, *args, code: int=400, **kwargs):
+    def __init__(self, message, *args, code: int=400, nbr_cols: int=0, nbr_rows: int=0, **kwargs):
         super().__init__(message, *args, code=code, **kwargs)
-        self.attr_stack.append([self.__TYPE, {}])
+        self.nbr_cols = nbr_cols
+        self.nbr_rows = nbr_rows
+        self.attr_stack.append([self.__TYPE, {
+            'nbr_cols': self.nbr_cols,
+            'nbr_rows': self.nbr_rows
+        }])
 
 
 class UnexpectedFormattingError(TabularRendererError):

mfr/extensions/tabular/render.py

@@ -46,22 +46,31 @@ def _render_grid(self, fp, ext, *args, **kwargs):  # assets_path, ext):
         size = settings.SMALL_TABLE
         self._renderer_tabular_metrics['size'] = 'small'
         self._renderer_tabular_metrics['nbr_sheets'] = len(sheets)
-        for sheet in sheets:
-            sheet = sheets[sheet]  # Sheets are stored in key-value pairs of the form {sheet: (col, row)}
-            if len(sheet[0]) > 9:  # Check the number of columns
+        for sheet_title in sheets:
+            sheet = sheets[sheet_title]
+
+            # sheet is a two-element list.  sheet[0] is a list of dicts containing metadata about
+            # the column headers.  Each dict contains four keys: `field`, `name`, `sortable`, `id`.
+            # sheet[1] is a list of dicts where each dict contains the row data.  The keys are the
+            # fields the data belongs to and the values are the data values.
+
+            nbr_cols = len(sheet[0])
+            if nbr_cols > 9:
                 size = settings.BIG_TABLE
                 self._renderer_tabular_metrics['size'] = 'big'
 
-            if len(sheet[0]) > settings.MAX_SIZE or len(sheet[1]) > settings.MAX_SIZE:
-                raise exceptions.TableTooBigError('Table is too large to render.', extension=ext)
+            nbr_rows = len(sheet[1])
+            if nbr_cols > settings.MAX_SIZE or nbr_rows > settings.MAX_SIZE:
+                raise exceptions.TableTooBigError('Table is too large to render.', extension=ext,
+                                                  nbr_cols=nbr_cols, nbr_rows=nbr_rows)
 
         return sheets, size
 
     def _populate_data(self, fp, ext):
         """Determine the appropriate library and use it to populate rows and columns
         :param fp: file pointer
         :param ext: file extension
-        :return: tuple of column headers and row data
+        :return: a dict mapping sheet titles to tuples of column headers and row data
         """
         function_preference = settings.LIBS.get(ext.lower())
 

mfr/extensions/tabular/settings.py

@@ -4,7 +4,7 @@
 
 config = settings.child('TABULAR_EXTENSION_CONFIG')
 
-MAX_SIZE = int(config.get('MAX_SIZE', 10000))
+MAX_SIZE = int(config.get('MAX_SIZE', 10000))  # max number of rows or columns allowed.
 TABLE_WIDTH = int(config.get('TABLE_WIDTH', 700))
 TABLE_HEIGHT = int(config.get('TABLE_HEIGHT', 600))