bpo-42967: Fix urllib.parse docs and make logic clearer (GH-24536)

Author: Fidget-Spinner

Doc/library/urllib.parse.rst

@@ -190,7 +190,8 @@ or on combining URL components into a URL string.
  read. If set, then throws a :exc:`ValueError` if there are more than
  *max_num_fields* fields read.
 
- The optional argument *separator* is the symbol to use for separating the query arguments. It defaults to `&`.
+ The optional argument *separator* is the symbol to use for separating the
+ query arguments. It defaults to ``&``.
 
  Use the :func:`urllib.parse.urlencode` function (with the ``doseq``
  parameter set to ``True``) to convert such dictionaries into query
@@ -204,8 +205,10 @@ or on combining URL components into a URL string.
  Added *max_num_fields* parameter.
 
  .. versionchanged:: 3.10
- Added *separator* parameter with the default value of `&`. Python versions earlier than Python 3.10 allowed using both ";" and "&" as
- query parameter separator. This has been changed to allow only a single separator key, with "&" as the default separator.
+ Added *separator* parameter with the default value of ``&``. Python
+ versions earlier than Python 3.10 allowed using both ``;`` and ``&`` as
+ query parameter separator. This has been changed to allow only a single
+ separator key, with ``&`` as the default separator.
 
 
 .. function:: parse_qsl(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None, separator='&')
@@ -232,7 +235,8 @@ or on combining URL components into a URL string.
  read. If set, then throws a :exc:`ValueError` if there are more than
  *max_num_fields* fields read.
 
- The optional argument *separator* is the symbol to use for separating the query arguments. It defaults to `&`.
+ The optional argument *separator* is the symbol to use for separating the
+ query arguments. It defaults to ``&``.
 
  Use the :func:`urllib.parse.urlencode` function to convert such lists of pairs into
  query strings.
@@ -244,8 +248,10 @@ or on combining URL components into a URL string.
  Added *max_num_fields* parameter.
 
  .. versionchanged:: 3.10
- Added *separator* parameter with the default value of `&`. Python versions earlier than Python 3.10 allowed using both ";" and "&" as
- query parameter separator. This has been changed to allow only a single separator key, with "&" as the default separator.
+ Added *separator* parameter with the default value of ``&``. Python
+ versions earlier than Python 3.10 allowed using both ``;`` and ``&`` as
+ query parameter separator. This has been changed to allow only a single
+ separator key, with ``&`` as the default separator.
 
 
 .. function:: urlunparse(parts)

Doc/whatsnew/3.6.rst

@@ -2447,11 +2447,11 @@ details, see the documentation for ``loop.create_datagram_endpoint()``.
 Notable changes in Python 3.6.13
 ================================
 
-Earlier Python versions allowed using both ";" and "&" as
+Earlier Python versions allowed using both ``;`` and ``&`` as
 query parameter separators in :func:`urllib.parse.parse_qs` and
 :func:`urllib.parse.parse_qsl`. Due to security concerns, and to conform with
 newer W3C recommendations, this has been changed to allow only a single
-separator key, with "&" as the default. This change also affects
+separator key, with ``&`` as the default. This change also affects
 :func:`cgi.parse` and :func:`cgi.parse_multipart` as they use the affected
 functions internally. For more details, please see their respective
 documentation.

Doc/whatsnew/3.8.rst

@@ -2238,11 +2238,11 @@ details, see the documentation for ``loop.create_datagram_endpoint()``.
 Notable changes in Python 3.8.8
 ===============================
 
-Earlier Python versions allowed using both ";" and "&" as
+Earlier Python versions allowed using both ``;`` and ``&`` as
 query parameter separators in :func:`urllib.parse.parse_qs` and
 :func:`urllib.parse.parse_qsl`. Due to security concerns, and to conform with
 newer W3C recommendations, this has been changed to allow only a single
-separator key, with "&" as the default. This change also affects
+separator key, with ``&`` as the default. This change also affects
 :func:`cgi.parse` and :func:`cgi.parse_multipart` as they use the affected
 functions internally. For more details, please see their respective
 documentation.

Doc/whatsnew/3.9.rst

@@ -1520,11 +1520,11 @@ become a :exc:`TypeError` in Python 3.10.
 urllib.parse
 ------------
 
-Earlier Python versions allowed using both ";" and "&" as
+Earlier Python versions allowed using both ``;`` and ``&`` as
 query parameter separators in :func:`urllib.parse.parse_qs` and
 :func:`urllib.parse.parse_qsl`. Due to security concerns, and to conform with
 newer W3C recommendations, this has been changed to allow only a single
-separator key, with "&" as the default. This change also affects
+separator key, with ``&`` as the default. This change also affects
 :func:`cgi.parse` and :func:`cgi.parse_multipart` as they use the affected
 functions internally. For more details, please see their respective
 documentation.

Lib/urllib/parse.py

@@ -734,8 +734,7 @@ def parse_qsl(qs, keep_blank_values=False, strict_parsing=False,
  """
  qs, _coerce_result = _coerce_args(qs)
 
- if not separator or (not isinstance(separator, str)
- and not isinstance(separator, bytes)):
+ if not separator or (not isinstance(separator, (str, bytes))):
  raise ValueError("Separator must be of type string or bytes.")
 
  # If max_num_fields is defined then check that the number of fields