Rework as a docs-only change

Author: vasiliyk

Doc/library/urllib.request.rst

@@ -246,14 +246,17 @@ The following classes are provided:
    server, or ``None`` if no such data is needed.  Currently HTTP
    requests are the only ones that use *data*.  The supported object
    types include bytes, file-like objects, and iterables of bytes-like objects.
-   Mappings, such as :class:`dict`, are not accepted and raise
-   :exc:`TypeError`.
    If no ``Content-Length`` nor ``Transfer-Encoding`` header field
    has been provided, :class:`HTTPHandler` will set these headers according
    to the type of *data*.  ``Content-Length`` will be used to send
    bytes objects, while ``Transfer-Encoding: chunked`` as specified in
    :rfc:`7230`, Section 3.3.1 will be used to send files and other iterables.
 
+   *data* is not serialized before it is sent: the elements of an iterable
+   are sent as is, so a :class:`dict` yields only its keys.  Structured
+   data such as a JSON object must be encoded to bytes first, for example
+   with :func:`json.dumps`.
+
    For an HTTP POST request method, *data* should be a buffer in the
    standard :mimetype:`application/x-www-form-urlencoded` format.  The
    :func:`urllib.parse.urlencode` function takes a mapping or sequence
@@ -320,9 +323,6 @@ The following classes are provided:
       provided and *data* is neither ``None`` nor a bytes object.
       Fall back to use chunked transfer encoding instead.
 
-   .. versionchanged:: next
-      Raise :exc:`TypeError` if *data* is a mapping.
-
 .. class:: OpenerDirector()
 
    The :class:`OpenerDirector` class opens URLs via :class:`BaseHandler`\ s chained

Lib/test/test_urllib2.py

@@ -11,7 +11,6 @@
 import ftplib
 import socket
 import array
-import collections
 import sys
 import tempfile
 import subprocess
@@ -997,12 +996,6 @@ def test_http(self):
         req = Request("http://example.com/","badpost")
         self.assertRaises(TypeError, h.do_request_, req)
 
-        # Check for TypeError on request data which is a mapping.
-        for data in ({'a': 1}, collections.UserDict({'a': 1})):
-            req = Request("http://example.com/", data)
-            with self.assertRaisesRegex(TypeError, type(data).__name__):
-                h.do_request_(req)
-
         # check adding of standard headers
         o.addheaders = [("Spam", "eggs")]
         for data in b"", None:  # POST, GET

Lib/urllib/request.py

@@ -95,7 +95,7 @@
 import sys
 import time
 import tempfile
-from collections.abc import Mapping
+
 
 from urllib.error import URLError, HTTPError, ContentTooShortError
 from urllib.parse import (
@@ -1261,10 +1261,9 @@ def do_request_(self, request):
 
         if request.data is not None:  # POST
             data = request.data
-            if isinstance(data, (str, Mapping)):
+            if isinstance(data, str):
                 msg = "POST data should be bytes, an iterable of bytes, " \
-                      "or a file object. It cannot be of type " \
-                      f"{type(data).__name__}."
+                      "or a file object. It cannot be of type str."
                 raise TypeError(msg)
             if not request.has_header('Content-type'):
                 request.add_unredirected_header(