diff --git a/Lib/configparser.py b/Lib/configparser.py
index 3c452afe8..88015ef60 100644
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -618,7 +618,8 @@ class RawConfigParser(MutableMapping):
     _OPT_TMPL = r"""
         (?P<option>                        # very permissive!
             (?:(?!{delim})\S)*             # non-delimiter non-whitespace
-            (?:\s+(?:(?!{delim})\S)+)*)    # optionally more words
+            (?:(?:(?!{delim})\s)+          # optionally more
+             (?:(?!{delim})\S)+)*)         #   space-separated words
         \s*(?P<vi>{delim})\s*              # any number of space/tab,
                                            # followed by any of the
                                            # allowed delimiters,
@@ -628,7 +629,8 @@ class RawConfigParser(MutableMapping):
     _OPT_NV_TMPL = r"""
         (?P<option>                        # very permissive!
             (?:(?!{delim})\S)*             # non-delimiter non-whitespace
-            (?:\s+(?:(?!{delim})\S)+)*)    # optionally more words
+            (?:(?:(?!{delim})\s)+          # optionally more
+             (?:(?!{delim})\S)+)*)         #   space-separated words
         \s*(?:                             # any number of space/tab,
         (?P<vi>{delim})\s*                 # optionally followed by
                                            # any of the allowed
diff --git a/Lib/csv.py b/Lib/csv.py
index 5d15344ea..4940aa28d 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -81,8 +81,6 @@ __all__ = ["QUOTE_MINIMAL", "QUOTE_ALL", "QUOTE_NONNUMERIC", "QUOTE_NONE",
            "unregister_dialect", "DictReader", "DictWriter",
            "unix_dialect"]
 
-__version__ = "1.0"
-
 
 class Dialect:
     """Describe a CSV dialect.
@@ -378,31 +376,33 @@ class Sniffer:
         try and evaluate the smallest portion of the data possible, evaluating
         additional chunks as necessary.
         """
+        from collections import Counter, defaultdict
 
         data = list(filter(None, data.split('\n')))
 
-        ascii = [chr(c) for c in range(127)] # 7-bit ASCII
-
         # build frequency tables
         chunkLength = min(10, len(data))
         iteration = 0
-        charFrequency = {}
+        num_lines = 0
+        # {char -> {count_per_line -> num_lines_with_that_count}}
+        char_frequency = defaultdict(Counter)
         modes = {}
         delims = {}
         start, end = 0, chunkLength
         while start < len(data):
             iteration += 1
             for line in data[start:end]:
-                for char in ascii:
-                    metaFrequency = charFrequency.get(char, {})
-                    # must count even if frequency is 0
-                    freq = line.count(char)
-                    # value is the mode
-                    metaFrequency[freq] = metaFrequency.get(freq, 0) + 1
-                    charFrequency[char] = metaFrequency
+                num_lines += 1
+                for char, count in Counter(line).items():
+                    if char.isascii():
+                        char_frequency[char][count] += 1
 
-            for char in charFrequency.keys():
-                items = list(charFrequency[char].items())
+            for char, counts in char_frequency.items():
+                items = list(counts.items())
+                missed_lines = num_lines - sum(counts.values())
+                if missed_lines:
+                    # Store the number of lines 'char' was missing from.
+                    items.append((0, missed_lines))
                 if len(items) == 1 and items[0][0] == 0:
                     continue
                 # get the mode of the frequencies
@@ -525,3 +525,12 @@ class Sniffer:
                     hasHeader -= 1
 
         return hasHeader > 0
+
+
+def __getattr__(name):
+    if name == "__version__":
+        from warnings import _deprecated
+
+        _deprecated("__version__", remove=(3, 20))
+        return "1.0"  # Do not change
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/Lib/fractions.py b/Lib/fractions.py
index a497ee199..c1b12e7a1 100644
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -242,11 +242,6 @@ class Fraction(numbers.Rational):
                 self._denominator = 1
                 return self
 
-            elif isinstance(numerator, numbers.Rational):
-                self._numerator = numerator.numerator
-                self._denominator = numerator.denominator
-                return self
-
             elif (isinstance(numerator, float) or
                   (not isinstance(numerator, type) and
                    hasattr(numerator, 'as_integer_ratio'))):
@@ -282,6 +277,11 @@ class Fraction(numbers.Rational):
                 if m.group('sign') == '-':
                     numerator = -numerator
 
+            elif isinstance(numerator, numbers.Rational):
+                self._numerator = numerator.numerator
+                self._denominator = numerator.denominator
+                return self
+
             else:
                 raise TypeError("argument should be a string or a Rational "
                                 "instance or have the as_integer_ratio() method")
diff --git a/Lib/graphlib.py b/Lib/graphlib.py
index 7961c9c5c..af5245ccb 100644
--- a/Lib/graphlib.py
+++ b/Lib/graphlib.py
@@ -199,6 +199,7 @@ class TopologicalSorter:
                     self._ready_nodes.append(successor)
             self._nfinished += 1
 
+    # See note "On Finding Cycles" at the bottom.
     def _find_cycle(self):
         n2i = self._node2info
         stack = []
@@ -212,8 +213,6 @@ class TopologicalSorter:
 
             while True:
                 if node in seen:
-                    # If we have seen already the node and is in the
-                    # current stack we have found a cycle.
                     if node in node2stacki:
                         return stack[node2stacki[node] :] + [node]
                     # else go on to get next successor
@@ -228,11 +227,15 @@ class TopologicalSorter:
                 while stack:
                     try:
                         node = itstack[-1]()
-                        break
+                        break # resume at top of "while True:"
                     except StopIteration:
+                        # no more successors; pop the stack
+                        # and continue looking up
                         del node2stacki[stack.pop()]
                         itstack.pop()
                 else:
+                    # stack is empty; look for a fresh node to
+                    # start over from (a node not yet in seen)
                     break
         return None
 
@@ -252,3 +255,55 @@ class TopologicalSorter:
             self.done(*node_group)
 
     __class_getitem__ = classmethod(GenericAlias)
+
+
+# On Finding Cycles
+# -----------------
+# There is a (at least one) total order if and only if the graph is
+# acyclic.
+#
+# When it is cyclic, "there's a cycle - somewhere!" isn't very helpful.
+# In theory, it would be most helpful to partition the graph into
+# strongly connected components (SCCs) and display those with more than
+# one node. Then all cycles could easily be identified "by eyeball".
+#
+# That's a lot of work, though, and we can get most of the benefit much
+# more easily just by showing a single specific cycle.
+#
+# Approaches to that are based on breadth first or depth first search
+# (BFS or DFS). BFS is most natural, which can easily be arranged to
+# find a shortest-possible cycle. But memory burden can be high, because
+# every path-in-progress has to keep its own idea of what "the path" is
+# so far.
+#
+# DFS is much easier on RAM, only requiring keeping track of _the_ path
+# from the starting node to the current node at the current recursion
+# level. But there may be any number of nodes, and so there's no bound
+# on recursion depth short of the total number of nodes.
+#
+# So we use an iterative version of DFS, keeping an exploit list
+# (`stack`) of the path so far. A parallel stack (`itstack`) holds the
+# `__next__` method of an iterator over the current level's node's
+# successors, so when backtracking to a shallower level we can just call
+# that to get the node's next successor. This is state that a recursive
+# version would implicitly store in a `for` loop's internals.
+#
+# `seen()` is a set recording which nodes have already been, at some
+# time, pushed on the stack. If a node has been pushed on the stack, DFS
+# will find any cycle it's part of, so there's no need to ever look at
+# it again.
+#
+# Finally, `node2stacki` maps a node to its index on the current stack,
+# for and only for nodes currently _on_ the stack. If a successor to be
+# pushed on the stack is in that dict, the node is already on the path,
+# at that index. The cycle is then `stack[that_index :] + [node]`.
+#
+# As is often the case when removing recursion, the control flow looks a
+# bit off. The "while True:" loop here rarely actually loops - it's only
+# looking to go "up the stack" until finding a level that has another
+# successor to consider, emulating a chain of returns in a recursive
+# version.
+#
+# Worst cases: O(V+E) for time, and O(V) for memory, where V is the
+# number of nodes and E the number of edges (which may be quadratic in
+# V!). It requires care to ensure these bounds are met.
diff --git a/Lib/heapq.py b/Lib/heapq.py
index 17f62dd2d..a3af6dc05 100644
--- a/Lib/heapq.py
+++ b/Lib/heapq.py
@@ -494,7 +494,7 @@ def nsmallest(n, iterable, key=None):
         pass
     else:
         if n >= size:
-            return sorted(iterable, key=key)[:n]
+            return sorted(iterable, key=key)
 
     # When key is none, use simpler decoration
     if key is None:
@@ -511,7 +511,7 @@ def nsmallest(n, iterable, key=None):
         for elem in it:
             if elem < top:
                 _heapreplace(result, (elem, order))
-                top, _order = result[0]
+                top = result[0][0]
                 order += 1
         result.sort()
         return [elem for (elem, order) in result]
@@ -529,7 +529,7 @@ def nsmallest(n, iterable, key=None):
         k = key(elem)
         if k < top:
             _heapreplace(result, (k, order, elem))
-            top, _order, _elem = result[0]
+            top = result[0][0]
             order += 1
     result.sort()
     return [elem for (k, order, elem) in result]
@@ -554,7 +554,7 @@ def nlargest(n, iterable, key=None):
         pass
     else:
         if n >= size:
-            return sorted(iterable, key=key, reverse=True)[:n]
+            return sorted(iterable, key=key, reverse=True)
 
     # When key is none, use simpler decoration
     if key is None:
@@ -569,7 +569,7 @@ def nlargest(n, iterable, key=None):
         for elem in it:
             if top < elem:
                 _heapreplace(result, (elem, order))
-                top, _order = result[0]
+                top = result[0][0]
                 order -= 1
         result.sort(reverse=True)
         return [elem for (elem, order) in result]
@@ -587,7 +587,7 @@ def nlargest(n, iterable, key=None):
         k = key(elem)
         if top < k:
             _heapreplace(result, (k, order, elem))
-            top, _order, _elem = result[0]
+            top = result[0][0]
             order -= 1
     result.sort(reverse=True)
     return [elem for (k, order, elem) in result]
diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index ca732e4f2..f1062a8cd 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -8,9 +8,6 @@ and networks.
 
 """
 
-__version__ = '1.0'
-
-
 import functools
 
 IPV4LENGTH = 32
@@ -1479,6 +1476,10 @@ class IPv4Interface(IPv4Address):
         return '%s/%s' % (self._string_from_ip_int(self._ip),
                           self.hostmask)
 
+    @property
+    def is_unspecified(self):
+        return self._ip == 0 and self.network.is_unspecified
+
 
 class IPv4Network(_BaseV4, _BaseNetwork):
 
@@ -2415,3 +2416,12 @@ class _IPv6Constants:
 
 IPv6Address._constants = _IPv6Constants
 IPv6Network._constants = _IPv6Constants
+
+
+def __getattr__(name):
+    if name == "__version__":
+        from warnings import _deprecated
+
+        _deprecated("__version__", remove=(3, 20))
+        return "1.0"  # Do not change
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/Lib/netrc.py b/Lib/netrc.py
index bd003e80a..cb1e3782a 100644
--- a/Lib/netrc.py
+++ b/Lib/netrc.py
@@ -48,11 +48,12 @@ class _netrclex:
     def get_token(self):
         if self.pushback:
             return self.pushback.pop(0)
-        token = ""
+        token = None
         fiter = iter(self._read_char, "")
         for ch in fiter:
             if ch in self.whitespace:
                 continue
+            token = ""
             if ch == '"':
                 for ch in fiter:
                     if ch == '"':
@@ -95,10 +96,10 @@ class netrc:
         while 1:
             # Look for a machine, default, or macdef top-level keyword
             saved_lineno = lexer.lineno
-            toplevel = tt = lexer.get_token()
-            if not tt:
+            tt = lexer.get_token()
+            if tt is None:
                 break
-            elif tt[0] == '#':
+            elif tt.startswith('#'):
                 if lexer.lineno == saved_lineno and len(tt) == 1:
                     lexer.instream.readline()
                 continue
@@ -135,40 +136,45 @@ class netrc:
             while 1:
                 prev_lineno = lexer.lineno
                 tt = lexer.get_token()
-                if tt.startswith('#'):
+                if tt is not None and tt.startswith('#'):
                     if lexer.lineno == prev_lineno:
                         lexer.instream.readline()
                     continue
-                if tt in {'', 'machine', 'default', 'macdef'}:
+                if tt in {None, 'machine', 'default', 'macdef'}:
                     self.hosts[entryname] = (login, account, password)
                     lexer.push_token(tt)
                     break
                 elif tt == 'login' or tt == 'user':
-                    login = lexer.get_token()
+                    login = lexer.get_token() or ''
                 elif tt == 'account':
-                    account = lexer.get_token()
+                    account = lexer.get_token() or ''
                 elif tt == 'password':
-                    password = lexer.get_token()
+                    password = lexer.get_token() or ''
                 else:
                     raise NetrcParseError("bad follower token %r" % tt,
                                           file, lexer.lineno)
-            self._security_check(fp, default_netrc, self.hosts[entryname][0])
 
-    def _security_check(self, fp, default_netrc, login):
-        if _can_security_check() and default_netrc and login != "anonymous":
-            prop = os.fstat(fp.fileno())
-            current_user_id = os.getuid()
-            if prop.st_uid != current_user_id:
-                fowner = _getpwuid(prop.st_uid)
-                user = _getpwuid(current_user_id)
-                raise NetrcParseError(
-                    (f"~/.netrc file owner ({fowner}, {user}) does not match"
-                     " current user"))
-            if (prop.st_mode & (stat.S_IRWXG | stat.S_IRWXO)):
-                raise NetrcParseError(
-                    "~/.netrc access too permissive: access"
-                    " permissions must restrict access to only"
-                    " the owner")
+        if _can_security_check() and default_netrc:
+            for entry in self.hosts.values():
+                if entry[0] != "anonymous":
+                    # Raises on security issue; once passed once can exit.
+                    self._security_check(fp)
+                    return
+
+    def _security_check(self, fp):
+        prop = os.fstat(fp.fileno())
+        current_user_id = os.getuid()
+        if prop.st_uid != current_user_id:
+            fowner = _getpwuid(prop.st_uid)
+            user = _getpwuid(current_user_id)
+            raise NetrcParseError(
+                f"~/.netrc file owner ({fowner}) does not match"
+                f" current user ({user})")
+        if (prop.st_mode & (stat.S_IRWXG | stat.S_IRWXO)):
+            raise NetrcParseError(
+                "~/.netrc access too permissive: access"
+                " permissions must restrict access to only"
+                " the owner")
 
     def authenticators(self, host):
         """Return a (user, account, password) tuple for given host."""
diff --git a/Lib/plistlib.py b/Lib/plistlib.py
index c3aee1e15..93f3ef5e3 100644
--- a/Lib/plistlib.py
+++ b/Lib/plistlib.py
@@ -2,7 +2,7 @@ r"""plistlib.py -- a tool to generate and parse MacOSX .plist files.
 
 The property list (.plist) file format is a simple XML pickle supporting
 basic object types, like dictionaries, lists, numbers and strings.
-Usually the top level object is a dictionary.
+Usually the top level object is a dictionary or a frozen dictionary.
 
 To write out a plist file, use the dump(value, file)
 function. 'value' is the top level object, 'file' is
@@ -122,13 +122,7 @@ _controlCharPat = re.compile(
     r"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f]")
 
 def _encode_base64(s, maxlinelength=76):
-    # copied from base64.encodebytes(), with added maxlinelength argument
-    maxbinsize = (maxlinelength//4)*3
-    pieces = []
-    for i in range(0, len(s), maxbinsize):
-        chunk = s[i : i + maxbinsize]
-        pieces.append(binascii.b2a_base64(chunk))
-    return b''.join(pieces)
+    return binascii.b2a_base64(s, wrapcol=maxlinelength, newline=False)
 
 def _decode_base64(s):
     if isinstance(s, str):
@@ -363,7 +357,7 @@ class _PlistWriter(_DumbXMLWriter):
         elif isinstance(value, float):
             self.simple_element("real", repr(value))
 
-        elif isinstance(value, dict):
+        elif isinstance(value, (dict, frozendict)):
             self.write_dict(value)
 
         elif isinstance(value, (bytes, bytearray)):
@@ -382,11 +376,10 @@ class _PlistWriter(_DumbXMLWriter):
     def write_bytes(self, data):
         self.begin_element("data")
         self._indent_level -= 1
-        maxlinelength = max(
-            16,
-            76 - len((self.indent * self._indent_level).expandtabs()))
-
-        for line in _encode_base64(data, maxlinelength).split(b"\n"):
+        wrapcol = 76 - len((self.indent * self._indent_level).expandtabs())
+        wrapcol = max(16, wrapcol)
+        encoded = binascii.b2a_base64(data, wrapcol=wrapcol, newline=False)
+        for line in encoded.split(b"\n"):
             if line:
                 self.writeln(line)
         self._indent_level += 1
@@ -460,7 +453,7 @@ class InvalidFileException (ValueError):
     def __init__(self, message="Invalid file"):
         ValueError.__init__(self, message)
 
-_BINARY_FORMAT = {1: 'B', 2: 'H', 4: 'L', 8: 'Q'}
+_BINARY_FORMAT = frozendict({1: 'B', 2: 'H', 4: 'L', 8: 'Q'})
 
 _undefined = object()
 
@@ -722,7 +715,7 @@ class _BinaryPlistWriter (object):
             self._objidtable[id(value)] = refnum
 
         # And finally recurse into containers
-        if isinstance(value, dict):
+        if isinstance(value, (dict, frozendict)):
             keys = []
             values = []
             items = value.items()
@@ -843,7 +836,7 @@ class _BinaryPlistWriter (object):
             self._write_size(0xA0, s)
             self._fp.write(struct.pack('>' + self._ref_format * s, *refs))
 
-        elif isinstance(value, dict):
+        elif isinstance(value, (dict, frozendict)):
             keyRefs, valRefs = [], []
 
             if self._sort_keys:
@@ -876,18 +869,18 @@ def _is_fmt_binary(header):
 # Generic bits
 #
 
-_FORMATS={
-    FMT_XML: dict(
+_FORMATS=frozendict({
+    FMT_XML: frozendict(
         detect=_is_fmt_xml,
         parser=_PlistParser,
         writer=_PlistWriter,
     ),
-    FMT_BINARY: dict(
+    FMT_BINARY: frozendict(
         detect=_is_fmt_binary,
         parser=_BinaryPlistParser,
         writer=_BinaryPlistWriter,
     )
-}
+})
 
 
 def load(fp, *, fmt=None, dict_type=dict, aware_datetime=False):
diff --git a/Lib/statistics.py b/Lib/statistics.py
index 26cf92552..01ca6c51d 100644
--- a/Lib/statistics.py
+++ b/Lib/statistics.py
@@ -136,7 +136,7 @@ import sys
 
 from fractions import Fraction
 from decimal import Decimal
-from itertools import count, groupby, repeat
+from itertools import compress, count, groupby, repeat
 from bisect import bisect_left, bisect_right
 from math import hypot, sqrt, fabs, exp, erfc, tau, log, fsum, sumprod
 from math import isfinite, isinf, pi, cos, sin, tan, cosh, asin, atan, acos
@@ -145,6 +145,7 @@ from operator import itemgetter
 from collections import Counter, namedtuple, defaultdict
 
 _SQRT2 = sqrt(2.0)
+_SQRT2PI = sqrt(tau)
 _random = random
 
 ## Exceptions ##############################################################
@@ -194,9 +195,9 @@ def fmean(data, weights=None):
             n = len(data)
         except TypeError:
             # Handle iterators that do not define __len__().
-            counter = count()
-            total = fsum(map(itemgetter(0), zip(data, counter)))
-            n = next(counter)
+            counter = count(1)
+            total = fsum(compress(data, counter))
+            n = next(counter) - 1
         else:
             total = fsum(data)
 
@@ -247,7 +248,7 @@ def geometric_mean(data):
             elif x == 0.0:
                 found_zero = True
             else:
-                raise StatisticsError('No negative inputs allowed', x)
+                raise StatisticsError(f'No negative inputs allowed: {x!r}')
 
     total = fsum(map(log, count_positive(data)))
 
@@ -1257,11 +1258,11 @@ class NormalDist:
 
     def pdf(self, x):
         "Probability density function.  P(x <= X < x+dx) / dx"
-        variance = self._sigma * self._sigma
-        if not variance:
+        sigma = self._sigma
+        if not sigma:
             raise StatisticsError('pdf() not defined when sigma is zero')
-        diff = x - self._mu
-        return exp(diff * diff / (-2.0 * variance)) / sqrt(tau * variance)
+        z = (x - self._mu) / sigma
+        return exp(-0.5 * z * z) / (_SQRT2PI * sigma)
 
     def cdf(self, x):
         "Cumulative distribution function.  P(X <= x)"
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index 4783943f7..7d1e68fe3 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -43,7 +43,7 @@ class CfgParserTestCaseClass:
     default_section = configparser.DEFAULTSECT
     interpolation = configparser._UNSET
 
-    def newconfig(self, defaults=None):
+    def newconfig(self, defaults=None, **kwargs):
         arguments = dict(
             defaults=defaults,
             allow_no_value=self.allow_no_value,
@@ -56,6 +56,7 @@ class CfgParserTestCaseClass:
             default_section=self.default_section,
             interpolation=self.interpolation,
         )
+        arguments.update(kwargs)
         instance = self.config_class(**arguments)
         return instance
 
@@ -358,6 +359,32 @@ boolean {0[0]} NO
                 the larch {0[1]} 1
             """.format(self.delimiters)))
 
+    @support.subTests('data', [
+        'foo bar=baz',
+        'foo   bar=baz',
+        'foo=bar=baz',
+        'foo = bar=baz',
+        'foo\t \t=\t \tbar=baz',
+    ])
+    def test_space_delimiter(self, data):
+        # gh-156353: Space should be accepted as a delimiter
+        cf = self.newconfig(delimiters=(' ', '='))
+        cf.read_string(f"[all]\n{data}")
+        self.assertEqual(cf.options('all'), ['foo'])
+        self.assertEqual(cf.get('all', 'foo'), 'bar=baz')
+
+    @support.subTests('delimiter', ' =:;#x\t\0\N{RS}\N{CEDILLA}\N{CAT}')
+    @support.subTests('space_before', ['', ' ', '\t', ' \t'])
+    @support.subTests('space_after', ['', ' ', '\t', ' \t'])
+    def test_any_delimiter(self, delimiter, space_before, space_after):
+        cf = self.newconfig(
+            delimiters=(delimiter,),
+            inline_comment_prefixes=None,
+        )
+        cf.read_string(f"[all]\nfoo{space_before}{delimiter}{space_after}bar=baz")
+        self.assertEqual(cf.options('all'), ['foo'])
+        self.assertEqual(cf.get('all', 'foo'), 'bar=baz')
+
     def test_basic_from_dict(self):
         config = {
             "Foo Bar": {
@@ -1991,8 +2018,8 @@ class ConvertersTestCase(BasicTestCase, unittest.TestCase):
 
     config_class = configparser.ConfigParser
 
-    def newconfig(self, defaults=None):
-        instance = super().newconfig(defaults=defaults)
+    def newconfig(self, defaults=None, **kwargs):
+        instance = super().newconfig(defaults=defaults, **kwargs)
         instance.converters['list'] = lambda v: [e.strip() for e in v.split()
                                                  if e.strip()]
         return instance
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 21b02c2f0..a055aeb7b 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -1308,6 +1308,19 @@ class TestDialectValidity(unittest.TestCase):
                     self.assertRaises(ValueError, create_invalid, field_name, " ",
                                       skipinitialspace=True)
 
+    def test_dialect_getattr_non_attribute_error_propagates(self):
+        # gh-145966: non-AttributeError exceptions raised by __getattr__
+        # during dialect attribute lookup must propagate, not be silenced.
+        class BadDialect:
+            def __getattr__(self, name):
+                raise RuntimeError("boom")
+
+        with self.assertRaises(RuntimeError):
+            csv.reader([], dialect=BadDialect())
+
+        with self.assertRaises(RuntimeError):
+            csv.writer(StringIO(), dialect=BadDialect())
+
 
 class TestSniffer(unittest.TestCase):
     sample1 = """\
@@ -1502,6 +1515,56 @@ ghi\0jkl
         dialect = sniffer.sniff(self.sample9)
         self.assertTrue(dialect.doublequote)
 
+    def test_guess_delimiter_crlf_not_chosen(self):
+        # Ensure that we pick the real delimiter ("|") over "\r" in a tie.
+        sniffer = csv.Sniffer()
+        sample = "a|b\r\nc|d\r\ne|f\r\n"
+        self.assertEqual(sniffer.sniff(sample).delimiter, "|")
+        self.assertNotEqual(sniffer.sniff(sample).delimiter, "\r")
+
+    def test_zero_mode_tie_order_independence(self):
+        sniffer = csv.Sniffer()
+        # ":" appears in half the rows (1, 0, 1, 0) - a tie between
+        #     0 and 1 per line.
+        # "," appears once every row (true delimiter).
+        #
+        # Even if the zero-frequency bucket is appended vs. inserted, the tie
+        # yields an adjusted score of 0, so ":" should not be promoted and
+        # "," must be selected.
+        sample = (
+            "a,b:c\n"
+            "d,e\n"
+            "f,g:c\n"
+            "h,i\n"
+        )
+        dialect = sniffer.sniff(sample)
+        self.assertEqual(dialect.delimiter, ",")
+
+    def test_zero_mode_tie_order_comma_first(self):
+        sniffer = csv.Sniffer()
+        pattern = (
+            "a,b\n"
+            "c:d\n"
+            "e,f\n"
+            "g:h\n"
+        )
+        sample = pattern * 10
+        with self.assertRaisesRegex(csv.Error, "Could not determine delimiter"):
+            sniffer.sniff(sample)
+
+    def test_zero_mode_tie_order_colon_first(self):
+        sniffer = csv.Sniffer()
+        pattern = (
+            "a:b\n"
+            "c,d\n"
+            "e:f\n"
+            "g,h\n"
+        )
+        sample = pattern * 10
+        with self.assertRaisesRegex(csv.Error, "Could not determine delimiter"):
+            sniffer.sniff(sample)
+
+
     def test_sniff_regex_backtracking(self):
         # gh-109638: this artificial sample used to take minutes.
         sniffer = csv.Sniffer()
@@ -1719,5 +1782,16 @@ class MiscTestCase(unittest.TestCase):
             with self.subTest(tp=tp):
                 check_disallow_instantiation(self, tp)
 
+
+class TestModule(unittest.TestCase):
+    def test_deprecated__version__(self):
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            "'__version__' is deprecated and slated for removal in Python 3.20",
+        ) as cm:
+            getattr(csv, "__version__")
+        self.assertEqual(cm.filename, __file__)
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 8af91e857..3f017b97d 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -2303,6 +2303,10 @@ class IpaddrUnitTest(unittest.TestCase):
         self.assertEqual(False, ipaddress.ip_network('240.0.0.0').is_multicast)
         self.assertEqual(True, ipaddress.ip_network('240.0.0.0').is_reserved)
 
+        self.assertTrue(ipaddress.ip_interface('0.0.0.0/32').is_unspecified)
+        self.assertFalse(ipaddress.ip_interface('0.0.0.0/31').is_unspecified)
+        self.assertFalse(ipaddress.ip_interface('1.2.3.4/32').is_unspecified)
+
         self.assertEqual(True, ipaddress.ip_interface(
                 '192.168.1.1/17').is_private)
         self.assertEqual(False, ipaddress.ip_network('192.169.0.0').is_private)
@@ -2851,5 +2855,15 @@ class IpaddrUnitTest(unittest.TestCase):
         )
 
 
+class TestModule(unittest.TestCase):
+    def test_deprecated__version__(self):
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            "'__version__' is deprecated and slated for removal in Python 3.20",
+        ) as cm:
+            getattr(ipaddress, "__version__")
+        self.assertEqual(cm.filename, __file__)
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/test/test_netrc.py b/Lib/test/test_netrc.py
index 9d720f627..bbb49bf15 100644
--- a/Lib/test/test_netrc.py
+++ b/Lib/test/test_netrc.py
@@ -1,6 +1,9 @@
 import netrc, os, unittest, sys, textwrap
+from pathlib import Path
 from test import support
 from test.support import os_helper
+from unittest.mock import patch
+
 
 temp_filename = os_helper.TESTFN
 
@@ -59,6 +62,9 @@ class NetrcTestCase(unittest.TestCase):
             "machine host.domain.com login",
             "machine host.domain.com account",
             "machine host.domain.com password",
+            "machine host.domain.com login \"\"",
+            "machine host.domain.com account \"\"",
+            "machine host.domain.com password \"\"",
             "machine host.domain.com login \"\" account",
             "machine host.domain.com login \"\" password",
             "machine host.domain.com account \"\" password"
@@ -71,6 +77,9 @@ class NetrcTestCase(unittest.TestCase):
             "default login",
             "default account",
             "default password",
+            "default login \"\"",
+            "default account \"\"",
+            "default password \"\"",
             "default login \"\" account",
             "default login \"\" password",
             "default account \"\" password"
@@ -79,6 +88,15 @@ class NetrcTestCase(unittest.TestCase):
             nrc = self.make_nrc(item)
             self.assertEqual(nrc.hosts['default'], ('', '', ''))
 
+    def test_empty_quoted_token_is_not_eof(self):
+        data = (
+            '"" invalid',
+            'machine host.domain.com "" invalid',
+        )
+        for item in data:
+            with self.subTest(item=item):
+                self.assertRaises(netrc.NetrcParseError, self.make_nrc, item)
+
     def test_invalid_tokens(self):
         data = (
             "invalid host.domain.com",
@@ -309,6 +327,26 @@ class NetrcTestCase(unittest.TestCase):
             self.assertEqual(nrc.hosts['foo.domain.com'],
                              ('anonymous', '', 'pass'))
 
+    @unittest.skipUnless(os.name == 'posix', 'POSIX only test')
+    @unittest.skipUnless(hasattr(os, 'getuid'), "os.getuid is required")
+    @os_helper.skip_unless_working_chmod
+    def test_security_only_once(self):
+        # Make sure security check is only run once per parse when multiple
+        # entries are found.
+        with patch.object(netrc.netrc, "_security_check") as mock:
+            with os_helper.temp_dir() as tmp_dir:
+                netrc_path = Path(tmp_dir) / '.netrc'
+                netrc_path.write_text("""\
+                machine foo.domain.com login bar password pass
+                machine bar.domain.com login foo password pass
+                """)
+                netrc_path.chmod(0o600)
+                with os_helper.EnvironmentVarGuard() as environ:
+                    environ.set('HOME', tmp_dir)
+                    netrc.netrc()
+
+            mock.assert_called_once()
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Lib/test/test_plistlib.py b/Lib/test/test_plistlib.py
index 2dccee9c2..daceceb61 100644
--- a/Lib/test/test_plistlib.py
+++ b/Lib/test/test_plistlib.py
@@ -792,6 +792,25 @@ class TestPlistlib(unittest.TestCase):
                 })
                 self.assertIsNot(pl2['first'], pl2['second'])
 
+    def test_frozendict(self):
+        pl = frozendict(
+            aString="Doodah",
+            anInt=728,
+            aDict=frozendict(
+                anotherString="hello",
+                aTrueValue=True,
+            ),
+            aList=["A", "B", 12],
+        )
+
+        for fmt in ALL_FORMATS:
+            with self.subTest(fmt=fmt):
+                data = plistlib.dumps(pl, fmt=fmt)
+                pl2 = plistlib.loads(data)
+                self.assertEqual(pl2, dict(pl))
+                self.assertIsInstance(pl2, dict)
+                self.assertIsInstance(pl2['aDict'], dict)
+
     def test_controlcharacters(self):
         for i in range(128):
             c = chr(i)
diff --git a/Lib/test/test_statistics.py b/Lib/test/test_statistics.py
index e0b74432c..677a87b51 100644
--- a/Lib/test/test_statistics.py
+++ b/Lib/test/test_statistics.py
@@ -2496,8 +2496,7 @@ class TestKDE(unittest.TestCase):
 
         data = [-2.1, -1.3, -0.4, 1.9, 5.1, 6.2, 7.8, 14.3, 15.1, 15.3, 15.8, 17.0]
         xarr = [x / 10 for x in range(-100, 250)]
-        # TODO: RUSTPYTHON - n originally 1_000_000 in CPython implementation but sorting is slow
-        n = 30_000
+        n = 1_000_000
         h = 1.75
         dx = 0.1
 
@@ -2519,8 +2518,7 @@ class TestKDE(unittest.TestCase):
                 F_hat = statistics.kde(data, h, kernel, cumulative=True)
 
                 for x in xarr:
-                    # TODO : RUSTPYTHON - abs_tol=0.0005 in CPython implementation but smaller `n` increases variance
-                    self.assertTrue(math.isclose(p_observed(x), p_expected(x), abs_tol=0.005))
+                    self.assertTrue(math.isclose(p_observed(x), p_expected(x), abs_tol=0.0005))
 
         # Test online updates to data