diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index 41ee3d8..e07ab0d 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -155,7 +155,7 @@
    bytecode
       Python source code is compiled into bytecode, the internal representation
       of a Python program in the CPython interpreter.  The bytecode is also
-      cached in ``.pyc`` and ``.pyo`` files so that executing the same file is
+      cached in ``.pyc`` files so that executing the same file is
       faster the second time (recompilation from source to bytecode can be
       avoided).  This "intermediate language" is said to run on a
       :term:`virtual machine` that executes the machine code corresponding to
diff --git a/Doc/library/zipfile.rst b/Doc/library/zipfile.rst
index 4cde1dd..5b8c776 100644
--- a/Doc/library/zipfile.rst
+++ b/Doc/library/zipfile.rst
@@ -464,12 +464,12 @@
       added to the archive, compiling if necessary.
 
       If *pathname* is a file, the filename must end with :file:`.py`, and
-      just the (corresponding :file:`\*.py[co]`) file is added at the top level
+      just the (corresponding :file:`\*.pyc`) file is added at the top level
       (no path information).  If *pathname* is a file that does not end with
       :file:`.py`, a :exc:`RuntimeError` will be raised.  If it is a directory,
       and the directory is not a package directory, then all the files
-      :file:`\*.py[co]` are added at the top level.  If the directory is a
-      package directory, then all :file:`\*.py[co]` are added under the package
+      :file:`\*.pyc` are added at the top level.  If the directory is a
+      package directory, then all :file:`\*.pyc` are added under the package
       name as a file path, and if any subdirectories are package directories,
       all of these are added recursively.
 
diff --git a/Doc/library/zipimport.rst b/Doc/library/zipimport.rst
index 46b8c24..eaae2bb 100644
--- a/Doc/library/zipimport.rst
+++ b/Doc/library/zipimport.rst
@@ -9,7 +9,7 @@
 --------------
 
 This module adds the ability to import Python modules (:file:`\*.py`,
-:file:`\*.py[co]`) and packages from ZIP-format archives. It is usually not
+:file:`\*.pyc`) and packages from ZIP-format archives. It is usually not
 needed to use the :mod:`zipimport` module explicitly; it is automatically used
 by the built-in :keyword:`import` mechanism for :data:`sys.path` items that are paths
 to ZIP archives.
diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
index 195f63f..08dc311 100644
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -532,8 +532,8 @@
 
 .. envvar:: PYTHONDONTWRITEBYTECODE
 
-   If this is set to a non-empty string, Python won't try to write ``.pyc`` or
-   ``.pyo`` files on the import of source modules.  This is equivalent to
+   If this is set to a non-empty string, Python won't try to write ``.pyc``
+   files on the import of source modules.  This is equivalent to
    specifying the :option:`-B` option.
 
 
diff --git a/Modules/main.c b/Modules/main.c
index 633e757..0951b3f 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -53,7 +53,7 @@
 Options and arguments (and corresponding environment variables):\n\
 -b     : issue warnings about str(bytes_instance), str(bytearray_instance)\n\
          and comparing bytes/bytearray with str. (-bb: issue errors)\n\
--B     : don't write .py[co] files on import; also PYTHONDONTWRITEBYTECODE=x\n\
+-B     : don't write .pyc files on import; also PYTHONDONTWRITEBYTECODE=x\n\
 -c cmd : program passed in as string (terminates option list)\n\
 -d     : debug output from parser; also PYTHONDEBUG=x\n\
 -E     : ignore PYTHON* environment variables (such as PYTHONPATH)\n\
diff --git a/Modules/zipimport.c b/Modules/zipimport.c
index 18777b2..a74f6c7 100644
--- a/Modules/zipimport.c
+++ b/Modules/zipimport.c
@@ -1101,7 +1101,7 @@
     _Py_IDENTIFIER(decompress);
 
     if (importing_zlib != 0)
-        /* Someone has a zlib.py[co] in their Zip file;
+        /* Someone has a zlib.pyc in their Zip file;
            let's avoid a stack overflow. */
         return NULL;
     importing_zlib = 1;
@@ -1260,7 +1260,7 @@
     return d <= 1;
 }
 
-/* Given the contents of a .py[co] file in a buffer, unmarshal the data
+/* Given the contents of a .pyc file in a buffer, unmarshal the data
    and return the code object. Return None if it the magic word doesn't
    match (we do this instead of raising an exception as we fall back
    to .py if available and we don't want to mask other errors).
@@ -1400,7 +1400,7 @@
     PyObject *toc_entry, *stripped;
     time_t mtime;
 
-    /* strip 'c' or 'o' from *.py[co] */
+    /* strip 'c' from *.pyc */
     if (PyUnicode_READY(path) == -1)
         return (time_t)-1;
     stripped = PyUnicode_FromKindAndData(PyUnicode_KIND(path),
diff --git a/PC/getpathp.c b/PC/getpathp.c
index 1eeebfe..e7be704 100644
--- a/PC/getpathp.c
+++ b/PC/getpathp.c
@@ -185,7 +185,7 @@
    may extend 'filename' by one character.
 */
 static int
-ismodule(wchar_t *filename, int update_filename) /* Is module -- check for .pyc/.pyo too */
+ismodule(wchar_t *filename, int update_filename) /* Is module -- check for .pyc too */
 {
     size_t n;
 
@@ -196,7 +196,7 @@
     n = wcsnlen_s(filename, MAXPATHLEN+1);
     if (n < MAXPATHLEN) {
         int exist = 0;
-        filename[n] = Py_OptimizeFlag ? L'o' : L'c';
+        filename[n] = L'c';
         filename[n + 1] = L'\0';
         exist = exists(filename);
         if (!update_filename)
diff --git a/PCbuild/rmpyc.py b/PCbuild/rmpyc.py
index a1e75bb..0b58f68 100644
--- a/PCbuild/rmpyc.py
+++ b/PCbuild/rmpyc.py
@@ -1,25 +1,19 @@
-# Remove all the .pyc and .pyo files under ../Lib.
+# Remove all the .pyc files under ../Lib.
 
 
 def deltree(root):
     import os
     from os.path import join
 
-    npyc = npyo = 0
+    npyc = 0
     for root, dirs, files in os.walk(root):
         for name in files:
-            delete = False
-            if name.endswith('.pyc'):
-                delete = True
+            # to be thorough
+            if name.endswith(('.pyc', '.pyo')):
                 npyc += 1
-            elif name.endswith('.pyo'):
-                delete = True
-                npyo += 1
-
-            if delete:
                 os.remove(join(root, name))
 
-    return npyc, npyo
+    return npyc
 
-npyc, npyo = deltree("../Lib")
-print(npyc, ".pyc deleted,", npyo, ".pyo deleted")
+npyc = deltree("../Lib")
+print(npyc, ".pyc deleted")
diff --git a/PCbuild/rt.bat b/PCbuild/rt.bat
index b418a8b..b4b9bb1 100644
--- a/PCbuild/rt.bat
+++ b/PCbuild/rt.bat
@@ -4,8 +4,8 @@
 rem -d   Run Debug build (python_d.exe).  Else release build.
 rem -O   Run python.exe or python_d.exe (see -d) with -O.
 rem -q   "quick" -- normally the tests are run twice, the first time
-rem      after deleting all the .py[co] files reachable from Lib/.
-rem      -q runs the tests just once, and without deleting .py[co] files.
+rem      after deleting all the .pyc files reachable from Lib/.
+rem      -q runs the tests just once, and without deleting .pyc files.
 rem -x64 Run the 64-bit build of python (or python_d if -d was specified)
 rem      from the 'amd64' dir instead of the 32-bit build in this dir.
 rem All leading instances of these switches are shifted off, and
@@ -45,7 +45,7 @@
 set cmd="%exe%" %dashO% -u -Wd -E -bb -m test %regrtestargs%
 if defined qmode goto Qmode
 
-echo Deleting .pyc/.pyo files ...
+echo Deleting .pyc files ...
 "%exe%" "%pcbuild%rmpyc.py"
 
 echo Cleaning _pth files ...
@@ -55,7 +55,7 @@
 %cmd%
 @echo off
 
-echo About to run again without deleting .pyc/.pyo first:
+echo About to run again without deleting .pyc first:
 pause
 
 :Qmode
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 06030c3..afd4eb8 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -88,7 +88,7 @@
 int Py_UseClassExceptionsFlag = 1; /* Needed by bltinmodule.c: deprecated */
 int Py_FrozenFlag; /* Needed by getpath.c */
 int Py_IgnoreEnvironmentFlag; /* e.g. PYTHONPATH, PYTHONHOME */
-int Py_DontWriteBytecodeFlag; /* Suppress writing bytecode files (*.py[co]) */
+int Py_DontWriteBytecodeFlag; /* Suppress writing bytecode files (*.pyc) */
 int Py_NoUserSiteDirectory = 0; /* for -s and site.py */
 int Py_UnbufferedStdioFlag = 0; /* Unbuffered binary std{in,out,err} */
 int Py_HashRandomizationFlag = 0; /* for -R and PYTHONHASHSEED */