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/polish/pretty.py

@@ -2,10 +2,10 @@ import textwrap
 
 # from lxml.etree import Element
 
+from ebook_converter import constants as const
 from ebook_converter import force_unicode
-from ebook_converter.ebooks.oeb.base import (
-    serialize, OEB_DOCS, barename, OEB_STYLES, XPNSMAP, XHTML, SVG)
-from ebook_converter.ebooks.oeb.polish.container import OPF_NAMESPACES
+from ebook_converter.ebooks.oeb import parse_utils
+from ebook_converter.ebooks.oeb.base import serialize, OEB_DOCS, OEB_STYLES
 from ebook_converter.ebooks.oeb.polish.utils import guess_type
 from ebook_converter.utils.icu import sort_key
 
@@ -38,15 +38,15 @@ def pretty_opf(root):
     # Put all dc: tags first starting with title and author. Preserve order for
     # the rest.
     def dckey(x):
-        return {'title':0, 'creator':1}.get(barename(x.tag), 2)
-    for metadata in root.xpath('//opf:metadata', namespaces=OPF_NAMESPACES):
-        dc_tags = metadata.xpath('./*[namespace-uri()="%s"]' % OPF_NAMESPACES['dc'])
+        return {'title':0, 'creator':1}.get(parse_utils.barename(x.tag), 2)
+    for metadata in root.xpath('//opf:metadata', namespaces=const.OPF_NAMESPACES):
+        dc_tags = metadata.xpath('./*[namespace-uri()="%s"]' % const.DC11_NS)
         dc_tags.sort(key=dckey)
         for x in reversed(dc_tags):
             metadata.insert(0, x)
 
     # Group items in the manifest
-    spine_ids = root.xpath('//opf:spine/opf:itemref/@idref', namespaces=OPF_NAMESPACES)
+    spine_ids = root.xpath('//opf:spine/opf:itemref/@idref', namespaces=const.OPF_NAMESPACES)
     spine_ids = {x:i for i, x in enumerate(spine_ids)}
 
     def manifest_key(x):
@@ -75,7 +75,7 @@ def pretty_opf(root):
             i = sort_key(href)
         return (cat, i)
 
-    for manifest in root.xpath('//opf:manifest', namespaces=OPF_NAMESPACES):
+    for manifest in root.xpath('//opf:manifest', namespaces=const.OPF_NAMESPACES):
         try:
             children = sorted(manifest, key=manifest_key)
         except AttributeError:
@@ -84,19 +84,11 @@ def pretty_opf(root):
             manifest.insert(0, x)
 
 
-SVG_TAG = SVG('svg')
-BLOCK_TAGS = frozenset(map(XHTML, (
-    'address', 'article', 'aside', 'audio', 'blockquote', 'body', 'canvas', 'col', 'colgroup', 'dd',
-    'div', 'dl', 'dt', 'fieldset', 'figcaption', 'figure', 'footer', 'form',
-    'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'header', 'hgroup', 'hr', 'li',
-    'noscript', 'ol', 'output', 'p', 'pre', 'script', 'section', 'style', 'table', 'tbody', 'td',
-    'tfoot', 'th', 'thead', 'tr', 'ul', 'video', 'img'))) | {SVG_TAG}
-
 
 def isblock(x):
     if callable(x.tag) or not x.tag:
         return True
-    if x.tag in BLOCK_TAGS:
+    if x.tag in const.XHTML_BLOCK_TAGS | {const.SVG_SVG}:
         return True
     return False
 
@@ -141,12 +133,12 @@ def pretty_block(parent, level=1, indent='  '):
     that contain only other block tags '''
     if not parent.text or isspace(parent.text):
         parent.text = ''
-    nn = '\n' if hasattr(parent.tag, 'strip') and barename(parent.tag) in {'tr', 'td', 'th'} else '\n\n'
+    nn = '\n' if hasattr(parent.tag, 'strip') and parse_utils.barename(parent.tag) in {'tr', 'td', 'th'} else '\n\n'
     parent.text = parent.text + nn + (indent * level)
     for i, child in enumerate(parent):
         if isblock(child) and has_only_blocks(child):
             pretty_block(child, level=level+1, indent=indent)
-        elif child.tag == SVG_TAG:
+        elif child.tag == const.SVG_SVG:
             pretty_xml_tree(child, level=level, indent=indent)
         l = level
         if i == len(parent) - 1:
@@ -172,13 +164,13 @@ def pretty_html_tree(container, root):
         child.tail = '\n\n'
         if hasattr(child.tag, 'endswith') and child.tag.endswith('}head'):
             pretty_xml_tree(child)
-    for body in root.findall('h:body', namespaces=XPNSMAP):
+    for body in root.findall('h:body', namespaces=const.XPNSMAP):
         pretty_block(body)
         # Special case the handling of a body that contains a single block tag
         # with all content. In this case we prettify the containing block tag
         # even if it has non block children.
         if (len(body) == 1 and not callable(body[0].tag) and isblock(body[0]) and not has_only_blocks(
-            body[0]) and barename(body[0].tag) not in (
+            body[0]) and parse_utils.barename(body[0].tag) not in (
                     'pre', 'p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6') and len(body[0]) > 0):
             pretty_block(body[0], level=2)