diff --git a/src/sage/data_structures/bitset_base.pxd b/src/sage/data_structures/bitset_base.pxd
index 5a89b84fa3e..f932e894efe 100644
--- a/src/sage/data_structures/bitset_base.pxd
+++ b/src/sage/data_structures/bitset_base.pxd
@@ -37,7 +37,7 @@ from memory_allocator  cimport MemoryAllocator
 from memory_allocator.memory_allocator cimport align
 from cython.operator import preincrement as preinc
 
-from sage.cpython.string cimport char_to_str, str_to_bytes, bytes_to_str
+from sage.cpython.string cimport str_to_bytes, bytes_to_str
 from sage.libs.gmp.mpn cimport *
 from sage.libs.gmp.types cimport *
 from sage.data_structures.sparse_bitset cimport sparse_bitset_t
diff --git a/src/sage/interfaces/polymake.py b/src/sage/interfaces/polymake.py
index c459a7268e6..c857d14daf9 100644
--- a/src/sage/interfaces/polymake.py
+++ b/src/sage/interfaces/polymake.py
@@ -27,12 +27,9 @@
 
 import os
 import re
-import sys
-import time
 
 from .expect import Expect
 from .interface import (Interface, InterfaceElement, InterfaceFunctionElement)
-from sage.cpython.string import bytes_to_str, str_to_bytes
 from sage.misc.verbose import get_verbose
 from sage.misc.cachefunc import cached_method
 from sage.interfaces.tab_completion import ExtraTabCompletion
diff --git a/src/sage/matrix/matrix_gfpn_dense.pyx b/src/sage/matrix/matrix_gfpn_dense.pyx
index 1f9a3ecf725..14dcd5b589d 100644
--- a/src/sage/matrix/matrix_gfpn_dense.pyx
+++ b/src/sage/matrix/matrix_gfpn_dense.pyx
@@ -25,19 +25,18 @@ AUTHORS:
 
 """
 
-#*****************************************************************************
+# ***************************************************************************
 #       Copyright (C) 2015 Simon King <simon.king@uni-jena.de>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 2 of the License, or
 # (at your option) any later version.
-#                  http://www.gnu.org/licenses/
-#*****************************************************************************
+#                  https://www.gnu.org/licenses/
+# ***************************************************************************
 
 from cysignals.memory cimport check_realloc, check_malloc, sig_free
 from cpython.bytes cimport PyBytes_AsString, PyBytes_FromStringAndSize
-from sage.cpython.string cimport str_to_bytes
 from cysignals.signals cimport sig_on, sig_off, sig_check
 cimport cython
 
diff --git a/src/sage/misc/parser.pyx b/src/sage/misc/parser.pyx
index b979bd5907c..29d7a9cd7a0 100644
--- a/src/sage/misc/parser.pyx
+++ b/src/sage/misc/parser.pyx
@@ -10,16 +10,15 @@ AUTHOR:
 
 - Robert Bradshaw 2008-04 (initial version)
 """
-
-#*****************************************************************************
+# ***************************************************************************
 #       Copyright (C) 2008 Robert Bradshaw <robertwb@math.washington.edu>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 2 of the License, or
 # (at your option) any later version.
-#                  http://www.gnu.org/licenses/
-#*****************************************************************************
+#                  https://www.gnu.org/licenses/
+# ***************************************************************************
 
 from libc.string cimport strchr
 from cpython.bytes cimport PyBytes_FromStringAndSize
@@ -27,7 +26,6 @@ from cpython.list cimport PyList_Append
 
 import math
 
-from sage.cpython.string cimport str_to_bytes, bytes_to_str
 
 def foo(*args, **kwds):
     """