diff --git a/src/calibre/ebooks/conversion/__init__.py b/src/calibre/ebooks/conversion/__init__.py
index 675e233317..a8eb882a97 100644
--- a/src/calibre/ebooks/conversion/__init__.py
+++ b/src/calibre/ebooks/conversion/__init__.py
@@ -22,4 +22,4 @@ class ConversionUserFeedBack(Exception):
 
 # Ensure exception uses fully qualified name as this is used to detect it in
 # the GUI.
-ConversionUserFeedBack.__name__ = str('calibre.ebooks.conversion.ConversionUserFeedBack')
+ConversionUserFeedBack.__name__ = 'calibre.ebooks.conversion.ConversionUserFeedBack'
diff --git a/src/calibre/ebooks/docx/writer/container.py b/src/calibre/ebooks/docx/writer/container.py
index f747697689..b729ef73dc 100644
--- a/src/calibre/ebooks/docx/writer/container.py
+++ b/src/calibre/ebooks/docx/writer/container.py
@@ -243,7 +243,7 @@ class DOCX:
         namespaces = self.namespace.namespaces
         E = ElementMaker(namespace=namespaces['cp'], nsmap={x:namespaces[x] for x in 'cp dc dcterms xsi'.split()})
         cp = E.coreProperties(E.revision('1'), E.lastModifiedBy('calibre'))
-        ts = utcnow().isoformat(str('T')).rpartition('.')[0] + 'Z'
+        ts = utcnow().isoformat('T').rpartition('.')[0] + 'Z'
         for x in 'created modified'.split():
             x = cp.makeelement('{{{}}}{}'.format(namespaces['dcterms'], x), **{'{{{}}}type'.format(namespaces['xsi']):'dcterms:W3CDTF'})
             x.text = ts
diff --git a/src/calibre/ebooks/lrf/html/table.py b/src/calibre/ebooks/lrf/html/table.py
index a0d40999d3..82f65201fb 100644
--- a/src/calibre/ebooks/lrf/html/table.py
+++ b/src/calibre/ebooks/lrf/html/table.py
@@ -15,8 +15,8 @@ def ceil(num):
 
 def print_xml(elem):
     from calibre.ebooks.lrf.pylrs.pylrs import ElementWriter
-    elem = elem.toElement(str('utf8'))
-    ew = ElementWriter(elem, sourceEncoding=str('utf8'))
+    elem = elem.toElement('utf8')
+    ew = ElementWriter(elem, sourceEncoding='utf8')
     ew.write(sys.stdout)
     print()
 
diff --git a/src/calibre/ebooks/lrf/pylrs/pylrs.py b/src/calibre/ebooks/lrf/pylrs/pylrs.py
index 6cfe89d6e3..67c9a416bc 100644
--- a/src/calibre/ebooks/lrf/pylrs/pylrs.py
+++ b/src/calibre/ebooks/lrf/pylrs/pylrs.py
@@ -674,7 +674,7 @@ class Info(Delegator):
         # NB: generates an encoding attribute, which lrs2lrf does not
         tree = ElementTree(element=info)
         f = io.BytesIO()
-        tree.write(f, encoding=str('utf-8'), xml_declaration=True)
+        tree.write(f, encoding='utf-8', xml_declaration=True)
         xmlInfo = f.getvalue().decode('utf-8')
         xmlInfo = re.sub(r'<CThumbnail.*?>\n', '', xmlInfo)
         xmlInfo = xmlInfo.replace('SumPage>', 'Page>')
diff --git a/src/calibre/gui2/tweak_book/editor/syntax/javascript.py b/src/calibre/gui2/tweak_book/editor/syntax/javascript.py
index e63b78cdb7..48ae4109f6 100644
--- a/src/calibre/gui2/tweak_book/editor/syntax/javascript.py
+++ b/src/calibre/gui2/tweak_book/editor/syntax/javascript.py
@@ -31,39 +31,39 @@ class JavascriptLexer(RegexLexer):
     flags = re.UNICODE | re.MULTILINE
 
     tokens = {
-        str('commentsandwhitespace'): [
+        'commentsandwhitespace': [
             (r'\s+', Text),
             (r'<!--', Comment),
             (r'//.*?$', Comment.Single),
-            (r'/\*', Comment.Multiline, str('comment'))
+            (r'/\*', Comment.Multiline, 'comment')
         ],
-        str('comment'): [
+        'comment': [
             (r'[^*/]+', Comment.Multiline),
-            (r'\*/', Comment.Multiline, str('#pop')),
+            (r'\*/', Comment.Multiline, '#pop'),
             (r'[*/]', Comment.Multiline),
         ],
-        str('slashstartsregex'): [
-            include(str('commentsandwhitespace')),
+        'slashstartsregex': [
+            include('commentsandwhitespace'),
             (r'/(\\.|[^[/\\\n]|\[(\\.|[^\]\\\n])*])+/'
-             r'([gim]+\b|\B)', String.Regex, str('#pop')),
-            (r'(?=/)', Text, (str('#pop'), str('badregex'))),
-            default(str('#pop'))
+             r'([gim]+\b|\B)', String.Regex, '#pop'),
+            (r'(?=/)', Text, ('#pop', 'badregex')),
+            default('#pop')
         ],
-        str('badregex'): [
-            (r'\n', Text, str('#pop'))
+        'badregex': [
+            (r'\n', Text, '#pop')
         ],
-        str('root'): [
+        'root': [
             (r'\A#! ?/.*?\n', Comment),  # shebang lines are recognized by node.js
-            (r'^(?=\s|/|<!--)', Text, str('slashstartsregex')),
-            include(str('commentsandwhitespace')),
+            (r'^(?=\s|/|<!--)', Text, 'slashstartsregex'),
+            include('commentsandwhitespace'),
             (r'\+\+|--|~|&&|\?|:|\|\||\\(?=\n)|'
-             r'(<<|>>>?|==?|!=?|[-<>+*%&|^/])=?', Operator, str('slashstartsregex')),
-            (r'[{(\[;,]', Punctuation, str('slashstartsregex')),
+             r'(<<|>>>?|==?|!=?|[-<>+*%&|^/])=?', Operator, 'slashstartsregex'),
+            (r'[{(\[;,]', Punctuation, 'slashstartsregex'),
             (r'[})\].]', Punctuation),
             (r'(for|in|while|do|break|return|continue|switch|case|default|if|else|'
              r'throw|try|catch|finally|new|delete|typeof|instanceof|void|yield|'
-             r'this)\b', Keyword, str('slashstartsregex')),
-            (r'(var|let|with|function)\b', Keyword.Declaration, str('slashstartsregex')),
+             r'this)\b', Keyword, 'slashstartsregex'),
+            (r'(var|let|with|function)\b', Keyword.Declaration, 'slashstartsregex'),
             (r'(abstract|boolean|byte|char|class|const|debugger|double|enum|export|'
              r'extends|final|float|goto|implements|import|int|interface|long|native|'
              r'package|private|protected|public|short|static|super|synchronized|throws|'
diff --git a/src/calibre/library/sqlite.py b/src/calibre/library/sqlite.py
index 591462bc87..3b818823c2 100644
--- a/src/calibre/library/sqlite.py
+++ b/src/calibre/library/sqlite.py
@@ -77,7 +77,7 @@ def adapt_datetime(dt):
 
 
 sqlite.register_adapter(datetime, adapt_datetime)
-sqlite.register_converter(str('timestamp'), convert_timestamp)
+sqlite.register_converter('timestamp', convert_timestamp)
 
 
 def convert_bool(val):
@@ -85,8 +85,8 @@ def convert_bool(val):
 
 
 sqlite.register_adapter(bool, lambda x: 1 if x else 0)
-sqlite.register_converter(str('bool'), convert_bool)
-sqlite.register_converter(str('BOOL'), convert_bool)
+sqlite.register_converter('bool', convert_bool)
+sqlite.register_converter('BOOL', convert_bool)
 
 
 class DynamicFilter:
@@ -261,7 +261,7 @@ def do_connect(path, row_factory=None):
     conn.row_factory = sqlite.Row if row_factory else (lambda cursor, row: list(row))
     conn.create_aggregate('concat', 1, Concatenate)
     conn.create_aggregate('aum_sortconcat', 4, AumSortedConcatenate)
-    conn.create_collation(str('PYNOCASE'), partial(pynocase,
+    conn.create_collation('PYNOCASE', partial(pynocase,
         encoding=encoding))
     conn.create_function('title_sort', 1, title_sort)
     conn.create_function('author_to_author_sort', 1,
@@ -269,7 +269,7 @@ def do_connect(path, row_factory=None):
     conn.create_function('uuid4', 0, lambda: str(uuid.uuid4()))
     # Dummy functions for dynamically created filters
     conn.create_function('books_list_filter', 1, lambda x: 1)
-    conn.create_collation(str('icucollate'), icu_collator)
+    conn.create_collation('icucollate', icu_collator)
     plugins.load_sqlite3_extension(conn, 'sqlite_extension')
     return conn
 
diff --git a/src/calibre/utils/ipc/launch.py b/src/calibre/utils/ipc/launch.py
index 8dec659956..3dbb8de8ac 100644
--- a/src/calibre/utils/ipc/launch.py
+++ b/src/calibre/utils/ipc/launch.py
@@ -117,9 +117,9 @@ class Worker:
     @property
     def env(self):
         env = os.environ.copy()
-        env[str('CALIBRE_WORKER')] = environ_item('1')
+        env['CALIBRE_WORKER'] = environ_item('1')
         td = as_hex_unicode(msgpack_dumps(base_dir()))
-        env[str('CALIBRE_WORKER_TEMP_DIR')] = environ_item(td)
+        env['CALIBRE_WORKER_TEMP_DIR'] = environ_item(td)
         env.update(self._env)
         return env
 
@@ -180,7 +180,7 @@ class Worker:
         except OSError:
             # cwd no longer exists
             origwd = cwd or os.path.expanduser('~')
-        env[str('ORIGWD')] = environ_item(as_hex_unicode(msgpack_dumps(origwd)))
+        env['ORIGWD'] = environ_item(as_hex_unicode(msgpack_dumps(origwd)))
         _cwd = cwd
         if priority is None:
             priority = prefs['worker_process_priority']
diff --git a/src/calibre/utils/smtp.py b/src/calibre/utils/smtp.py
index 8783a86e64..4732e14521 100644
--- a/src/calibre/utils/smtp.py
+++ b/src/calibre/utils/smtp.py
@@ -157,7 +157,7 @@ def get_smtp_class(use_ssl=False, debuglevel=0):
     from polyglot import smtplib
     cls = smtplib.SMTP_SSL if use_ssl else smtplib.SMTP
     bases = (cls,)
-    return type(str('SMTP'), bases, {str('debuglevel'): debuglevel})
+    return type('SMTP', bases, {'debuglevel': debuglevel})
 
 
 def sendmail(msg, from_, to, localhost=None, verbose=0, timeout=None,