Delay load slow package level imports

src/calibre/ebooks/html/__init__.py

@@ -8,12 +8,13 @@ __docformat__ = 'restructuredtext en'
 
 import re
 
-from lxml.etree import tostring as _tostring
 
 def tostring(root, strip_comments=False, pretty_print=False):
     '''
     Serialize processed XHTML.
     '''
+    from lxml.etree import tostring as _tostring
+
     root.set('xmlns', 'http://www.w3.org/1999/xhtml')
     root.set('{http://www.w3.org/1999/xhtml}xlink', 'http://www.w3.org/1999/xlink')
     for x in root.iter():

src/calibre/ebooks/lrf/__init__.py

@@ -4,7 +4,6 @@ __copyright__ = '2008, Kovid Goyal <kovid at kovidgoyal.net>'
 This package contains logic to read and write LRF files.
 The LRF file format is documented at U{http://www.sven.de/librie/Librie/LrfFormat}.
 """
-from uuid import uuid4
 
 from calibre.ebooks.lrf.pylrs.pylrs import Book as _Book
 from calibre.ebooks.lrf.pylrs.pylrs import TextBlock, Header, \
@@ -60,6 +59,7 @@ def find_custom_fonts(options, logger):
 
 def Book(options, logger, font_delta=0, header=None,
          profile=PRS500_PROFILE, **settings):
+    from uuid import uuid4
     ps = {}
     ps['topmargin']      = options.top_margin
     ps['evensidemargin'] = options.left_margin

src/calibre/ebooks/pdb/__init__.py

@@ -7,7 +7,10 @@ __docformat__ = 'restructuredtext en'
 class PDBError(Exception):
     pass
 
+FORMAT_READERS = None
 
+def _import_readers():
+    global FORMAT_READERS
     from calibre.ebooks.pdb.ereader.reader import Reader as ereader_reader
     from calibre.ebooks.pdb.palmdoc.reader import Reader as palmdoc_reader
     from calibre.ebooks.pdb.ztxt.reader import Reader as ztxt_reader
@@ -23,6 +26,10 @@ FORMAT_READERS = {
         'DataPlkr': plucker_reader,
     }
 
+ALL_FORMAT_WRITERS = {'doc', 'ztxt', 'ereader'}
+FORMAT_WRITERS = None
+def _import_writers():
+    global FORMAT_WRITERS
     from calibre.ebooks.pdb.palmdoc.writer import Writer as palmdoc_writer
     from calibre.ebooks.pdb.ztxt.writer import Writer as ztxt_writer
     from calibre.ebooks.pdb.ereader.writer import Writer as ereader_writer
@@ -69,11 +76,17 @@ def get_reader(identity):
     '''
     Returns None if no reader is found for the identity.
     '''
+    global FORMAT_READERS
+    if FORMAT_READERS is None:
+        _import_readers()
     return FORMAT_READERS.get(identity, None)
 
 def get_writer(extension):
     '''
     Returns None if no writer is found for extension.
     '''
+    global FORMAT_WRITERS
+    if FORMAT_WRITERS is None:
+        _import_writers()
     return FORMAT_WRITERS.get(extension, None)
 

src/calibre/ebooks/pdb/output.py

@@ -8,7 +8,7 @@ import os
 
 from calibre.customize.conversion import OutputFormatPlugin, \
     OptionRecommendation
-from calibre.ebooks.pdb import PDBError, get_writer, FORMAT_WRITERS
+from calibre.ebooks.pdb import PDBError, get_writer, ALL_FORMAT_WRITERS
 
 class PDBOutput(OutputFormatPlugin):
 
@@ -19,9 +19,9 @@ class PDBOutput(OutputFormatPlugin):
     options = set([
         OptionRecommendation(name='format', recommended_value='doc',
             level=OptionRecommendation.LOW,
-            short_switch='f', choices=FORMAT_WRITERS.keys(),
+            short_switch='f', choices=list(ALL_FORMAT_WRITERS),
             help=(_('Format to use inside the pdb container. Choices are:')+\
-            ' %s' % FORMAT_WRITERS.keys())),
+            ' %s' % list(ALL_FORMAT_WRITERS))),
         OptionRecommendation(name='pdb_output_encoding', recommended_value='cp1252',
             level=OptionRecommendation.LOW,
             help=_('Specify the character encoding of the output document. ' \

src/calibre/web/feeds/__init__.py

@@ -7,9 +7,6 @@ Contains the logic for parsing feeds.
 '''
 import time, traceback, copy, re
 
-from lxml import html
-
-from calibre.web.feeds.feedparser import parse
 from calibre.utils.logging import default_log
 from calibre import entity_to_unicode, strftime
 from calibre.utils.date import dt_factory, utcnow, local_tz
@@ -18,6 +15,7 @@ from calibre.utils.cleantext import clean_ascii_chars
 class Article(object):
 
     def __init__(self, id, title, url, author, summary, published, content):
+        from lxml import html
         self.downloaded = False
         self.id = id
         self._title = title.strip() if title else title
@@ -320,6 +318,7 @@ def feed_from_xml(raw_xml, title=None, oldest_article=7,
                   max_articles_per_feed=100,
                   get_article_url=lambda item: item.get('link', None),
                   log=default_log):
+    from calibre.web.feeds.feedparser import parse
     # Handle unclosed escaped entities. They trip up feedparser and HBR for one
     # generates them
     raw_xml = re.sub(r'(&#\d+)([^0-9;])', r'\1;\2', raw_xml)