Use the real constants module.

This is progressing refactor of the calibre code to make it more
readable, and transform it to something more coherent.

In this patch, there are changes regarding imports for some modules,
instead of polluting namespace of each module with some other modules
symbols, which often were imported from other modules. Yuck.

ebook_converter/ebooks/oeb/transforms/structure.py

@@ -1,22 +1,19 @@
+import collections
 import re
-import uuid
 import urllib.parse
+import uuid
 
 from lxml import etree
-from collections import OrderedDict, Counter
 
-from ebook_converter.ebooks.oeb.base import XPNSMAP, TOC, XHTML, xml2text, barename
+from ebook_converter import constants as const
+from ebook_converter.ebooks.oeb import parse_utils
+from ebook_converter.ebooks.oeb.base import TOC, xml2text
 from ebook_converter.ebooks import ConversionError
 
 
-__license__ = 'GPL v3'
-__copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
-__docformat__ = 'restructuredtext en'
-
-
 def XPath(x):
     try:
-        return etree.XPath(x, namespaces=XPNSMAP)
+        return etree.XPath(x, namespaces=const.XPNSMAP)
     except etree.XPathSyntaxError:
         raise ConversionError(
         'The syntax of the XPath expression %s is invalid.' % repr(x))
@@ -84,7 +81,7 @@ class DetectStructure(object):
                     try:
                         prev = next(elem.itersiblings(tag=etree.Element,
                                 preceding=True))
-                        if (barename(elem.tag) in {'h1', 'h2'} and barename(
+                        if (parse_utils.barename(elem.tag) in {'h1', 'h2'} and parse_utils.barename(
                                 prev.tag) in {'h1', 'h2'} and (not prev.tail or
                                     not prev.tail.split())):
                             # We have two adjacent headings, do not put a page
@@ -165,7 +162,7 @@ class DetectStructure(object):
             chapter_mark = self.opts.chapter_mark
             page_break_before = 'display: block; page-break-before: always'
             page_break_after = 'display: block; page-break-after: always'
-            c = Counter()
+            c = collections.Counter()
             for item, elem in self.detected_chapters:
                 c[item] += 1
                 text = xml2text(elem).strip()
@@ -174,7 +171,7 @@ class DetectStructure(object):
                 if chapter_mark == 'none':
                     continue
                 if chapter_mark == 'rule':
-                    mark = elem.makeelement(XHTML('hr'))
+                    mark = elem.makeelement(const.XHTML_HR)
                 elif chapter_mark == 'pagebreak':
                     if c[item] < 3 and at_start(elem):
                         # For the first two elements in this item, check if they
@@ -184,9 +181,9 @@ class DetectStructure(object):
                         # feedbooks epubs match both a heading tag and its
                         # containing div with the default chapter expression.
                         continue
-                    mark = elem.makeelement(XHTML('div'), style=page_break_after)
+                    mark = elem.makeelement(const.XHTML_DIV, style=page_break_after)
                 else:  # chapter_mark == 'both':
-                    mark = elem.makeelement(XHTML('hr'), style=page_break_before)
+                    mark = elem.makeelement(const.XHTML_HR, style=page_break_before)
                 try:
                     elem.addprevious(mark)
                 except TypeError:
@@ -254,8 +251,8 @@ class DetectStructure(object):
         return text, href
 
     def add_leveled_toc_items(self):
-        added = OrderedDict()
-        added2 = OrderedDict()
+        added = collections.OrderedDict()
+        added2 = collections.OrderedDict()
         counter = 1
 
         def find_matches(expr, doc):