#18584: make doctest examples in email documentation pass.

With the exception of the 'as_string' call in the policy docs.
That one is a separate issue.

Note that when building the docs sphinx is complaining about
.. testcleanup:: being an invalid directive.  I don't know
why this is, as I'm following the sphinx docs...but fortunately
the action is to omit the text in the body, so the generated
documentation is correct.

Doc/library/email.iterators.rst

@@ -33,14 +33,22 @@ useful higher level iterations over message object trees.
    Thus, by default :func:`typed_subpart_iterator` returns each subpart that has a
    MIME type of :mimetype:`text/\*`.
 
+
 The following function has been added as a useful debugging tool.  It should
 *not* be considered part of the supported public interface for the package.
 
-
 .. function:: _structure(msg, fp=None, level=0, include_default=False)
 
    Prints an indented representation of the content types of the message object
-   structure.  For example::
+   structure.  For example:
+
+   .. testsetup::
+
+      >>> import email
+      >>> from email.iterators import _structure
+      >>> somefile = open('Lib/test/test_email/data/msg_02.txt')
+
+   .. doctest::
 
       >>> msg = email.message_from_file(somefile)
       >>> _structure(msg)
@@ -60,6 +68,10 @@ The following function has been added as a useful debugging tool.  It should
                   text/plain
           text/plain
 
+   .. testcleanup::
+
+      >>> somefile.close()
+
    Optional *fp* is a file-like object to print the output to.  It must be
    suitable for Python's :func:`print` function.  *level* is used internally.
    *include_default*, if true, prints the default type as well.

Doc/library/email.message.rst

@@ -513,16 +513,25 @@ Here are the methods of the :class:`Message` class:
       iterator in a ``for`` loop; each iteration returns the next subpart.
 
       Here's an example that prints the MIME type of every part of a multipart
-      message structure::
+      message structure:
 
-        >>> for part in msg.walk():
-        ...     print(part.get_content_type())
-        multipart/report
-        text/plain
-        message/delivery-status
-        text/plain
-        text/plain
-        message/rfc822
+       .. testsetup::
+
+            >>> from email import message_from_binary_file
+            >>> with open('Lib/test/test_email/data/msg_16.txt', 'rb') as f:
+            ...     msg = message_from_binary_file(f)
+
+       .. doctest::
+
+            >>> for part in msg.walk():
+            ...     print(part.get_content_type())
+            multipart/report
+            text/plain
+            message/delivery-status
+            text/plain
+            text/plain
+            message/rfc822
+            text/plain
 
    :class:`Message` objects can also optionally contain two instance attributes,
    which can be used when generating the plain text of a MIME message.

Doc/library/email.policy.rst

@@ -56,19 +56,42 @@ same keyword arguments as the class constructor and returning a new
 attributes values changed.
 
 As an example, the following code could be used to read an email message from a
-file on disk and pass it to the system ``sendmail`` program on a Unix system::
+file on disk and pass it to the system ``sendmail`` program on a Unix system:
 
-   >>> from email import msg_from_binary_file
+.. testsetup::
+
+   >>> from unittest import mock
+   >>> mocker = mock.patch('subprocess.Popen')
+   >>> m = mocker.start()
+   >>> proc = mock.MagicMock()
+   >>> m.return_value = proc
+   >>> proc.stdin.close.return_value = None
+   >>> mymsg = open('mymsg.txt', 'w')
+   >>> mymsg.write('To: abc@xyz.com\n\n')
+   17
+   >>> mymsg.flush()
+
+.. doctest::
+
+   >>> from email import message_from_binary_file
    >>> from email.generator import BytesGenerator
+   >>> from email import policy
    >>> from subprocess import Popen, PIPE
-   >>> with open('mymsg.txt', 'b') as f:
-   ...     msg = msg_from_binary_file(f)
-   >>> p = Popen(['sendmail', msg['To'][0].address], stdin=PIPE)
+   >>> with open('mymsg.txt', 'rb') as f:
+   ...     msg = message_from_binary_file(f, policy=policy.default)
+   >>> p = Popen(['sendmail', msg['To'].addresses[0]], stdin=PIPE)
    >>> g = BytesGenerator(p.stdin, policy=msg.policy.clone(linesep='\r\n'))
    >>> g.flatten(msg)
    >>> p.stdin.close()
    >>> rc = p.wait()
 
+.. testcleanup::
+
+   >>> mymsg.close()
+   >>> mocker.stop()
+   >>> import os
+   >>> os.remove('mymsg.txt')
+
 Here we are telling :class:`~email.generator.BytesGenerator` to use the RFC
 correct line separator characters when creating the binary string to feed into
 ``sendmail's`` ``stdin``, where the default policy would use ``\n`` line
@@ -82,22 +105,22 @@ separators for the platform on which it is running::
 
    >>> import os
    >>> with open('converted.txt', 'wb') as f:
-   ...     f.write(msg.as_string(policy=msg.policy.clone(linesep=os.linesep))
+   ...     f.write(msg.as_string(policy=msg.policy.clone(linesep=os.linesep)))
 
 Policy objects can also be combined using the addition operator, producing a
 policy object whose settings are a combination of the non-default values of the
 summed objects::
 
-   >>> compat_SMTP = email.policy.clone(linesep='\r\n')
-   >>> compat_strict = email.policy.clone(raise_on_defect=True)
+   >>> compat_SMTP = policy.compat32.clone(linesep='\r\n')
+   >>> compat_strict = policy.compat32.clone(raise_on_defect=True)
    >>> compat_strict_SMTP = compat_SMTP + compat_strict
 
 This operation is not commutative; that is, the order in which the objects are
 added matters.  To illustrate::
 
-   >>> policy100 = compat32.clone(max_line_length=100)
-   >>> policy80 = compat32.clone(max_line_length=80)
-   >>> apolicy = policy100 + Policy80
+   >>> policy100 = policy.compat32.clone(max_line_length=100)
+   >>> policy80 = policy.compat32.clone(max_line_length=80)
+   >>> apolicy = policy100 + policy80
    >>> apolicy.max_line_length
    80
    >>> apolicy = policy80 + policy100