Book list: Allow changing the font used for any column to bold and/or italic by right clicking on the column header and choosing "Change font style". Note that this setting is per-library so it has to be done once for the book list in every calibre library. Fixes #1758434 [[enhancement] individual column font choice](https://bugs.launchpad.net/calibre/+bug/1758434)

src/calibre/db/backend.py

@@ -49,8 +49,8 @@ Differences in semantics from pysqlite:
     3. There is no executescript
 
 '''
-CUSTOM_DATA_TYPES = frozenset(['rating', 'text', 'comments', 'datetime',
+CUSTOM_DATA_TYPES = frozenset(('rating', 'text', 'comments', 'datetime',
-    'int', 'float', 'bool', 'series', 'composite', 'enumeration'])
+    'int', 'float', 'bool', 'series', 'composite', 'enumeration'))
 WINDOWS_RESERVED_NAMES = frozenset('CON PRN AUX NUL COM1 COM2 COM3 COM4 COM5 COM6 COM7 COM8 COM9 LPT1 LPT2 LPT3 LPT4 LPT5 LPT6 LPT7 LPT8 LPT9'.split())
 
 
@@ -479,6 +479,7 @@ class DB(object):
         defs['field_under_covers_in_grid'] = 'title'
         defs['cover_browser_title_template'] = '{title}'
         defs['cover_browser_subtitle_field'] = 'rating'
+        defs['styled_columns'] = {}
 
         # Migrate the bool tristate tweak
         defs['bools_are_tristate'] = \

src/calibre/gui2/library/models.py

@@ -9,7 +9,7 @@ import functools, re, os, traceback, errno, time
 from collections import defaultdict, namedtuple
 from itertools import groupby
 
-from PyQt5.Qt import (QAbstractTableModel, Qt, pyqtSignal, QIcon, QImage,
+from PyQt5.Qt import (QAbstractTableModel, Qt, pyqtSignal, QIcon, QImage, QFont,
         QModelIndex, QDateTime, QColor, QPixmap, QPainter, QApplication)
 
 from calibre import fit_image, force_unicode
@@ -175,6 +175,14 @@ class BooksModel(QAbstractTableModel):  # {{{
 
     def __init__(self, parent=None, buffer=40):
         QAbstractTableModel.__init__(self, parent)
+        base_font = parent.font() if parent else QApplication.instance().font()
+        self.bold_font = QFont(base_font)
+        self.bold_font.setBold(True)
+        self.italic_font = QFont(base_font)
+        self.italic_font.setItalic(True)
+        self.bi_font = QFont(self.bold_font)
+        self.bi_font.setItalic(True)
+        self.styled_columns = {}
         self.orig_headers = {
                         'title'     : _("Title"),
                         'ondevice'   : _("On Device"),
@@ -258,6 +266,21 @@ class BooksModel(QAbstractTableModel):  # {{{
                 self.dataChanged.emit(self.index(row, col), self.index(row,
                     col))
 
+    def change_column_font(self, colname, font_type):
+        if colname in self.column_map and font_type in ('normal', 'bold', 'italic', 'bi'):
+            db = self.db.new_api
+            old = db.pref('styled_columns', {})
+            old.pop(colname, None)
+            self.styled_columns.pop(colname, None)
+            if font_type != 'normal':
+                self.styled_columns[colname] = getattr(self, '{}_font'.format(font_type))
+                old[colname] = font_type
+            self.db.new_api.set_pref('styled_columns', old)
+            col = self.column_map.index(colname)
+            for row in xrange(self.rowCount(QModelIndex())):
+                self.dataChanged.emit(self.index(row, col), self.index(row,
+                    col))
+
     def is_custom_column(self, cc_label):
         try:
             return cc_label in self.custom_columns
@@ -280,6 +303,10 @@ class BooksModel(QAbstractTableModel):  # {{{
 
     def set_database(self, db):
         self.ids_to_highlight = []
+
+        if db:
+            style_map = {'bold': self.bold_font, 'bi': self.bi_font, 'italic': self.italic_font}
+            self.styled_columns = {k: style_map.get(v, None) for k, v in db.new_api.pref('styled_columns', {}).iteritems()}
         self.alignment_map = {}
         self.ids_to_highlight_set = set()
         self.current_highlighted_idx = None
@@ -968,6 +995,9 @@ class BooksModel(QAbstractTableModel):  # {{{
             ans = Qt.AlignVCenter | ALIGNMENT_MAP[self.alignment_map.get(cname,
                 'left')]
             return (ans)
+        elif role == Qt.FontRole and self.styled_columns:
+            cname = self.column_map[index.column()]
+            return self.styled_columns.get(cname)
         # elif role == Qt.ToolTipRole and index.isValid():
         #    if self.column_map[index.column()] in self.editable_cols:
         #        return (_("Double click to <b>edit</b> me<br><br>"))

src/calibre/gui2/library/views.py

@@ -403,6 +403,8 @@ class BooksView(QTableView):  # {{{
         elif action.startswith('align_'):
             alignment = action.partition('_')[-1]
             self._model.change_alignment(column, alignment)
+        elif action.startswith('font_'):
+            self._model.change_column_font(column, action[len('font_'):])
         elif action == 'quickview':
             from calibre.gui2.actions.show_quickview import get_quickview_action_plugin
             qv = get_quickview_action_plugin()
@@ -437,6 +439,18 @@ class BooksView(QTableView):  # {{{
                     if al == x:
                         a.setCheckable(True)
                         a.setChecked(True)
+            if not isinstance(view, DeviceBooksView):
+                col_font = self._model.styled_columns.get(col)
+                m = ans.addMenu(_('Change font style for %s') % name)
+                for x, t, f in (
+                        ('normal', _('Normal font'), None), ('bold', _('Bold Font'), self._model.bold_font),
+                        ('italic', _('Italic font'), self._model.italic_font), ('bi', _('Bold and Italic font'), self._model.bi_font),
+                ):
+                    a = m.addAction(t, partial(handler, action='font_' + x))
+                    if f is col_font:
+                        a.setCheckable(True)
+                        a.setChecked(True)
+
         if self.is_library_view:
             if self._model.db.field_metadata[col]['is_category']:
                 act = ans.addAction(_('Quickview column %s') % name, partial(handler, action='quickview'))