In default branch:

$ grep -Er '(^|[[:space:]])an? the($|[[:space:]])' *
Doc/c-api/structures.rst::c:type:`PyObject\*`, it is common that the method implementation uses a the
Include/dynamic_annotations.h:     is about to be reused, or when a the locking discipline for a variable
Include/unicodeobject.h:/* Initializes the canonical string representation from a the deprecated
Lib/lib2to3/fixes/fix_exitfunc.py:        # First, find a the sys import. We'll just hope it's global scope.
Lib/socket.py:        Create a socket object from a the bytes object returned by
Lib/http/cookiejar.py:    """Return string representation of Cookie in an the LWP cookie file format.
Modules/_ctypes/_ctypes.c:       A Pointer instance must keep a the value it points to alive.  So, a

$ grep -Er '(^|[[:space:]])the an?($|[[:space:]])' *
Doc/library/unittest.mock.rst:being looked up on the a module and so we have to patch ``a.SomeClass`` instead::
Doc/c-api/init.rst:   Return the a pointer to the first :c:type:`PyThreadState` object in the list of
Doc/c-api/exceptions.rst:      case of a class exception, or it may the a subclass of the expected exception.)
Doc/distutils/apiref.rst:   *base_dir* is just the a name of a directory which doesn't necessarily exist
Lib/test/test_argparse.py:    """Tests the an optional action that is required"""
Lib/ssl.py:        """Return the a list of ciphers shared by the client during the
Lib/distutils/dir_util.py:    'base_dir' is just the a name of a directory which doesn't necessarily

'the a module' in Doc/library/unittest.mock.rst probably should be 'the ``a`` module'.
'may the a' in Doc/c-api/exceptions.rst should be 'may be a'.