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/metadata/utils.py

@@ -1,12 +1,13 @@
 from collections import namedtuple
 
+from lxml import etree
+
 from ebook_converter.ebooks.chardet import xml_to_unicode
-from ebook_converter.ebooks.oeb.base import OPF
+from ebook_converter.ebooks.oeb import base
 from ebook_converter.ebooks.oeb.polish.utils import guess_type
 from ebook_converter.spell import parse_lang_code
 from ebook_converter.utils.cleantext import clean_xml_chars
 from ebook_converter.utils.localization import lang_as_iso639_1
-from ebook_converter.utils.xml_parse import safe_xml_fromstring
 
 
 OPFVersion = namedtuple('OPFVersion', 'major minor patch')
@@ -35,23 +36,26 @@ def parse_opf(stream_or_path):
     raw = stream.read()
     if not raw:
         raise ValueError('Empty file: '+getattr(stream, 'name', 'stream'))
-    raw, encoding = xml_to_unicode(raw, strip_encoding_pats=True, resolve_entities=True, assume_utf8=True)
+    raw, encoding = xml_to_unicode(raw, strip_encoding_pats=True,
+                                   resolve_entities=True, assume_utf8=True)
     raw = raw[raw.find('<'):]
-    root = safe_xml_fromstring(clean_xml_chars(raw))
+    root = etree.fromstring(clean_xml_chars(raw))
     if root is None:
         raise ValueError('Not an OPF file')
     return root
 
 
 def normalize_languages(opf_languages, mi_languages):
-    ' Preserve original country codes and use 2-letter lang codes where possible '
+    """
+    Preserve original country codes and use 2-letter lang codes where possible
+    """
     def parse(x):
         try:
             return parse_lang_code(x)
         except ValueError:
             return None
     opf_languages = filter(None, map(parse, opf_languages))
-    cc_map = {c.langcode:c.countrycode for c in opf_languages}
+    cc_map = {c.langcode: c.countrycode for c in opf_languages}
     mi_languages = filter(None, map(parse, mi_languages))
 
     def norm(x):
@@ -83,9 +87,9 @@ def create_manifest_item(root, href_template, id_template, media_type=None):
     all_hrefs = frozenset(root.xpath('//*/@href'))
     href = ensure_unique(href_template, all_hrefs)
     item_id = ensure_unique(id_template, all_ids)
-    manifest = root.find(OPF('manifest'))
+    manifest = root.find(base.tag('opf', 'manifest'))
     if manifest is not None:
-        i = manifest.makeelement(OPF('item'))
+        i = manifest.makeelement(base.tag('opf', 'item'))
         i.set('href', href), i.set('id', item_id)
         i.set('media-type', media_type or guess_type(href_template))
         manifest.append(i)
@@ -93,6 +97,7 @@ def create_manifest_item(root, href_template, id_template, media_type=None):
 
 
 def pretty_print_opf(root):
-    from ebook_converter.ebooks.oeb.polish.pretty import pretty_opf, pretty_xml_tree
+    from ebook_converter.ebooks.oeb.polish.pretty import pretty_opf, \
+            pretty_xml_tree
     pretty_opf(root)
     pretty_xml_tree(root)