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/rasterize.py

@@ -5,10 +5,8 @@ import os
 import re
 import urllib.parse
 
-# from PyQt5.Qt import (
-    # Qt, QByteArray, QBuffer, QIODevice, QColor, QImage, QPainter, QSvgRenderer)
-
-from ebook_converter.ebooks.oeb.base import XHTML, XLINK
+from ebook_converter import constants as const
+from ebook_converter.ebooks.oeb import base
 from ebook_converter.ebooks.oeb.base import SVG_MIME, PNG_MIME
 from ebook_converter.ebooks.oeb.base import xml2str, xpath
 from ebook_converter.ebooks.oeb.base import urlnormalize
@@ -17,10 +15,7 @@ from ebook_converter.ptempfile import PersistentTemporaryFile
 from ebook_converter.utils.imghdr import what
 
 
-__license__ = 'GPL v3'
-__copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
-
-IMAGE_TAGS = {XHTML('img'), XHTML('object')}
+IMAGE_TAGS = {base.tag('xhtml', 'img'), base.tag('xhtml', 'object')}
 KEEP_ATTRS = {'class', 'style', 'width', 'height', 'align'}
 
 
@@ -113,7 +108,7 @@ class SVGRasterizer(object):
             svg = item.data
         hrefs = self.oeb.manifest.hrefs
         for elem in xpath(svg, '//svg:*[@xl:href]'):
-            href = urlnormalize(elem.attrib[XLINK('href')])
+            href = urlnormalize(elem.attrib[base.tag('xlink', 'href')])
             path = urllib.parse.urldefrag(href)[0]
             if not path:
                 continue
@@ -126,7 +121,7 @@ class SVGRasterizer(object):
             with PersistentTemporaryFile(suffix='.'+ext) as pt:
                 pt.write(data)
                 self.temp_files.append(pt.name)
-            elem.attrib[XLINK('href')] = pt.name
+            elem.attrib[base.tag('xlink', 'href')] = pt.name
         return svg
 
     def stylizer(self, item):
@@ -171,7 +166,7 @@ class SVGRasterizer(object):
         href = os.path.splitext(item.href)[0] + '.png'
         id, href = manifest.generate(item.id, href)
         manifest.add(id, href, PNG_MIME, data=data)
-        img = elem.makeelement(XHTML('img'), src=item.relhref(href))
+        img = elem.makeelement(base.tag('xhtml', 'img'), src=item.relhref(href))
         elem.getparent().replace(elem, img)
         for prop in ('width', 'height'):
             if prop in elem.attrib:
@@ -208,7 +203,7 @@ class SVGRasterizer(object):
             id, href = manifest.generate(svgitem.id, href)
             manifest.add(id, href, PNG_MIME, data=data)
             self.images[key] = href
-        elem.tag = XHTML('img')
+        elem.tag = base.tag('xhtml', 'img')
         for attr in elem.attrib:
             if attr not in KEEP_ATTRS:
                 del elem.attrib[attr]