py3: use unicode literals for casting strings

Since unicode_type cannot be used in dynamically updated code, cast to
the same type as type('') -- which we know will be unicode because of
unicode_literals.

src/calibre/ebooks/metadata/sources/amazon.py

@@ -351,7 +351,7 @@ def parse_details(self, raw, root):
         if self.testing:
             import tempfile
             import uuid
-            with tempfile.NamedTemporaryFile(prefix=(asin or str(uuid.uuid4())) + '_',
+            with tempfile.NamedTemporaryFile(prefix=(asin or type('')(uuid.uuid4())) + '_',
                                              suffix='.html', delete=False) as f:
                 f.write(raw)
             print('Downloaded html for', asin, 'saved in', f.name)

src/calibre/ebooks/metadata/sources/edelweiss.py

@@ -139,7 +139,7 @@ def get_basic_data(browser, log, *skus):
             'orderID': '0',
             'mailingID': '',
             'tContentWidth': '926',
-            'originalOrder': ','.join(str(i) for i in range(len(skus))),
+            'originalOrder': ','.join(type('')(i) for i in range(len(skus))),
             'selectedOrderID': '0',
             'selectedSortColumn': '0',
             'listType': '1',
@@ -255,7 +255,7 @@ def create_query(self, log, title=None, authors=None, identifiers={}):
             return None
         params = {
             'q': (' '.join(keywords)).encode('utf-8'),
-            '_': str(int(time.time()))
+            '_': type('')(int(time.time()))
         }
         return BASE_URL+urlencode(params)
 

src/calibre/ebooks/metadata/sources/google.py

@@ -121,7 +121,7 @@ def get_text(extra, x):
     # ISBN
     isbns = []
     for x in identifier(extra):
-        t = str(x.text).strip()
+        t = type('')(x.text).strip()
         if t[:5].upper() in ('ISBN:', 'LCCN:', 'OCLC:'):
             if t[:5].upper() == 'ISBN:':
                 t = check_isbn(t[5:])