Fix usage of QApplication for PyQt 4.6, since in 4.6 the global application instance is garbage collected, we need to store it in a global variable

resources/recipes/economist.recipe

@@ -87,4 +87,6 @@ class Economist(BasicNewsRecipe):
                 feeds[key].append(article)
 
         ans = [(key, feeds[key]) for key in ans if feeds.has_key(key)]
+        if not ans:
+            raise Exception('Could not find any articles. Has your subscription expired?')
         return ans

src/calibre/ebooks/lrf/html/table_as_image.py

@@ -11,7 +11,6 @@ from PyQt4.Qt import QUrl, QApplication, QSize, QEventLoop, \
                      SIGNAL, QPainter, QImage, QObject, Qt
 from PyQt4.QtWebKit import QWebPage
 
-
 class HTMLTableRenderer(QObject):
 
     def __init__(self, html, base_dir, width, height, dpi, factor):
@@ -87,8 +86,9 @@ def render_table(soup, table, css, base_dir, width, height, dpi, factor=1.0):
     return images
 
 def do_render(html, base_dir, width, height, dpi, factor):
-    if QApplication.instance() is None:
-        QApplication([])
+    from calibre.gui2 import is_ok_to_use_qt
+    if not is_ok_to_use_qt():
+        raise Exception('Not OK to use Qt')
     tr = HTMLTableRenderer(html, base_dir, width, height, dpi, factor)
     tr.loop.exec_()
     return tr.images, tr.tdir

src/calibre/ebooks/oeb/transforms/rasterize.py

@@ -18,7 +18,6 @@ from PyQt4.QtGui import QColor
 from PyQt4.QtGui import QImage
 from PyQt4.QtGui import QPainter
 from PyQt4.QtSvg import QSvgRenderer
-from PyQt4.QtGui import QApplication
 from calibre.ebooks.oeb.base import XHTML, XLINK
 from calibre.ebooks.oeb.base import SVG_MIME, PNG_MIME
 from calibre.ebooks.oeb.base import xml2str, xpath
@@ -30,8 +29,9 @@ KEEP_ATTRS = set(['class', 'style', 'width', 'height', 'align'])
 
 class SVGRasterizer(object):
     def __init__(self):
-        if QApplication.instance() is None:
-            QApplication([])
+        from calibre.gui2 import is_ok_to_use_qt
+        if not is_ok_to_use_qt():
+            raise Exception('Not OK to use Qt')
 
     @classmethod
     def config(cls, cfg):

src/calibre/ebooks/pdf/writer.py

@@ -18,7 +18,7 @@ from calibre.ebooks.metadata import authors_to_string
 
 from PyQt4 import QtCore
 from PyQt4.Qt import QUrl, QEventLoop, SIGNAL, QObject, \
-    QApplication, QPrinter, QMetaObject, QSizeF, Qt
+    QPrinter, QMetaObject, QSizeF, Qt
 from PyQt4.QtWebKit import QWebView
 
 from pyPdf import PdfFileWriter, PdfFileReader
@@ -37,8 +37,9 @@ class PDFMetadata(object):
 
 class PDFWriter(QObject):
     def __init__(self, opts, log):
-        if QApplication.instance() is None:
-            QApplication([])
+        from calibre.gui2 import is_ok_to_use_qt
+        if not is_ok_to_use_qt():
+            raise Exception('Not OK to use Qt')
         QObject.__init__(self)
 
         self.logger = log

src/calibre/gui2/__init__.py

@@ -528,12 +528,14 @@ class Application(QApplication):
         if set_qt_translator(self._translator):
             self.installTranslator(self._translator)
 
+_store_app = None
+
 def is_ok_to_use_qt():
-    global gui_thread
+    global gui_thread, _store_app
     if islinux and ':' not in os.environ.get('DISPLAY', ''):
         return False
-    if QApplication.instance() is None:
-        QApplication([])
+    if _store_app is None and QApplication.instance() is None:
+        _store_app = QApplication([])
     if gui_thread is None:
         gui_thread = QThread.currentThread()
     return gui_thread is QThread.currentThread()

src/calibre/gui2/convert/font_key.py

@@ -98,7 +98,7 @@ class FontKeyChooser(QDialog, Ui_Dialog):
 
 
 if __name__ == '__main__':
-    from PyQt4.Qt import QApplication
-    QApplication([])
+    from calibre.gui2 import is_ok_to_use_qt
+    is_ok_to_use_qt()
     d = FontKeyChooser()
     d.exec_()

src/calibre/gui2/dialogs/scheduler.py

@@ -9,7 +9,7 @@ Scheduler for automated recipe downloads
 
 from datetime import datetime, timedelta
 
-from PyQt4.Qt import QDialog, QApplication, SIGNAL, Qt, QTime, QObject, QMenu, \
+from PyQt4.Qt import QDialog, SIGNAL, Qt, QTime, QObject, QMenu, \
         QAction, QIcon, QMutex, QTimer
 
 from calibre.gui2.dialogs.scheduler_ui import Ui_Dialog
@@ -306,7 +306,8 @@ class Scheduler(QObject):
             self.download(urn)
 
 if __name__ == '__main__':
-    QApplication([])
+    from calibre.gui2 import is_ok_to_use_qt
+    is_ok_to_use_qt()
     from calibre.library.database2 import LibraryDatabase2
     d = SchedulerDialog(RecipeModel(LibraryDatabase2('/home/kovid/documents/library')))
     d.exec_()

src/calibre/gui2/dialogs/user_profiles.py

@@ -314,8 +314,8 @@ class %(classname)s(%(base_class)s):
         self.source_code.setText('')
 
 if __name__ == '__main__':
-    from PyQt4.Qt import QApplication
-    QApplication([])
+    from calibre.gui2 import is_ok_to_use_qt
+    is_ok_to_use_qt()
     from calibre.library.database2 import LibraryDatabase2
     from calibre.web.feeds.recipes.model import RecipeModel
     d=UserProfiles(None, RecipeModel(LibraryDatabase2('/home/kovid/documents/library')))

src/calibre/gui2/status.py

@@ -282,9 +282,10 @@ class StatusBar(QStatusBar):
 
 if __name__ == '__main__':
     # Used to create the animated status icon
-    from PyQt4.Qt import QApplication, QPainter, QSvgRenderer, QColor
+    from PyQt4.Qt import QPainter, QSvgRenderer, QColor
     from subprocess import check_call
-    app = QApplication([])
+    from calibre.gui2 import is_ok_to_use_qt
+    is_ok_to_use_qt()
 
     def create_pixmaps(path, size=16, delta=20):
         r = QSvgRenderer(path)

src/calibre/gui2/viewer/printing.py

@@ -10,7 +10,7 @@ from BeautifulSoup import BeautifulSoup, Tag
 
 
 from PyQt4 import QtCore
-from PyQt4.Qt import QUrl, QEventLoop, SIGNAL,  QObject, QApplication, Qt, \
+from PyQt4.Qt import QUrl, QEventLoop, SIGNAL,  QObject, Qt, \
     QPrinter, QPrintPreviewDialog, QPrintDialog, QDialog, QMetaObject, Q_ARG
 from PyQt4.QtWebKit import QWebView
 
@@ -18,8 +18,9 @@ PRINTCSS = 'body{width:100%;margin:0;padding:0;font-family:Arial;color:#000;back
 
 class Printing(QObject):
     def __init__(self, spine, preview):
-        if QApplication.instance() is None:
-            QApplication([])
+        from calibre.gui2 import is_ok_to_use_qt
+        if not is_ok_to_use_qt():
+            raise Exception('Not OK to use Qt')
         QObject.__init__(self)
         self.loop = QEventLoop()