Import plugins from calibre.constants not calibre

src/calibre/devices/kindle/bookmark.py

@@ -306,7 +306,7 @@ def get_book_length(self):
             except:
                 pass
         elif self.bookmark_extension == 'pdr':
-            from calibre import plugins
+            from calibre.constants import plugins
             try:
                 self.book_length = plugins['pdfreflow'][0].get_numpages(open(book_fs).read())
             except :

src/calibre/ebooks/lit/lzx.py

@@ -7,7 +7,7 @@
 __license__   = 'GPL v3'
 __copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
 
-from calibre import plugins
+from calibre.constants import plugins
 
 _lzx, _error = plugins['lzx']
 if _lzx is None:

src/calibre/ebooks/lit/reader.py

@@ -17,7 +17,7 @@
 from calibre.ebooks.oeb.base import urlnormalize, xpath
 from calibre.ebooks.oeb.reader import OEBReader
 from calibre.ebooks import DRMError
-from calibre import plugins
+from calibre.constants import plugins
 from polyglot.builtins import codepoint_to_chr, unicode_type, string_or_bytes, range, itervalues
 from polyglot.urllib import unquote as urlunquote, urldefrag
 

src/calibre/ebooks/lit/writer.py

@@ -27,7 +27,7 @@
 from calibre.ebooks.oeb.stylizer import Stylizer
 from calibre.ebooks.lit.lzx import Compressor
 import calibre
-from calibre import plugins
+from calibre.constants import plugins
 msdes, msdeserror = plugins['msdes']
 import calibre.ebooks.lit.mssha1 as mssha1
 from polyglot.builtins import codepoint_to_chr, unicode_type, string_or_bytes, range, zip, native_string_type

src/calibre/gui2/cover_flow.py

@@ -14,7 +14,7 @@
 from PyQt5.Qt import (QImage, QSizePolicy, QTimer, QDialog, Qt, QSize, QAction,
         QStackedLayout, QLabel, pyqtSignal, QKeySequence, QFont, QApplication)
 
-from calibre import plugins
+from calibre.constants import plugins
 from calibre.ebooks.metadata import rating_to_stars
 from calibre.constants import islinux
 from calibre.gui2 import (config, available_height, available_width, gprefs,