Get rid of the superstitious "~" in dict hashing's "i = (~hash) & mask".

The comment following used to say:
	/* We use ~hash instead of hash, as degenerate hash functions, such
	   as for ints <sigh>, can have lots of leading zeros. It's not
	   really a performance risk, but better safe than sorry.
	   12-Dec-00 tim:  so ~hash produces lots of leading ones instead --
	   what's the gain? */
That is, there was never a good reason for doing it.  And to the contrary,
as explained on Python-Dev last December, it tended to make the *sum*
(i + incr) & mask (which is the first table index examined in case of
collison) the same "too often" across distinct hashes.

Changing to the simpler "i = hash & mask" reduced the number of string-dict
collisions (== # number of times we go around the lookup for-loop) from about
6 million to 5 million during a full run of the test suite (these are
approximate because the test suite does some random stuff from run to run).
The number of collisions in non-string dicts also decreased, but not as
dramatically.

Note that this may, for a given dict, change the order (wrt previous
releases) of entries exposed by .keys(), .values() and .items().  A number
of std tests suffered bogus failures as a result.  For dicts keyed by
small ints, or (less so) by characters, the order is much more likely to be
in increasing order of key now; e.g.,

>>> d = {}
>>> for i in range(10):
...    d[i] = i
...
>>> d
{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
>>>

Unfortunately. people may latch on to that in small examples and draw a
bogus conclusion.

test_support.py
    Moved test_extcall's sortdict() into test_support, made it stronger,
    and imported sortdict into other std tests that needed it.
test_unicode.py
    Excluced cp875 from the "roundtrip over range(128)" test, because
    cp875 doesn't have a well-defined inverse for unicode("?", "cp875").
    See Python-Dev for excruciating details.
Cookie.py
    Chaged various output functions to sort dicts before building
    strings from them.
test_extcall
    Fiddled the expected-result file.  This remains sensitive to native
    dict ordering, because, e.g., if there are multiple errors in a
    keyword-arg dict (and test_extcall sets up many cases like that), the
    specific error Python complains about first depends on native dict
    ordering.

Lib/Cookie.py

@@ -70,8 +70,8 @@ a dictionary.
    >>> C["fig"] = "newton"
    >>> C["sugar"] = "wafer"
    >>> print C
-   Set-Cookie: sugar=wafer;
    Set-Cookie: fig=newton;
+   Set-Cookie: sugar=wafer;
 
 Notice that the printable representation of a Cookie is the
 appropriate format for a Set-Cookie: header.  This is the
@@ -93,8 +93,8 @@ HTTP_COOKIE environment variable.
    >>> C = Cookie.SmartCookie()
    >>> C.load("chips=ahoy; vienna=finger")
    >>> print C
-   Set-Cookie: vienna=finger;
    Set-Cookie: chips=ahoy;
+   Set-Cookie: vienna=finger;
 
 The load() method is darn-tootin smart about identifying cookies
 within a string.  Escaped quotation marks, nested semicolons, and other
@@ -493,7 +493,9 @@ class Morsel(UserDict):
         # Now add any defined attributes
         if attrs is None:
             attrs = self._reserved_keys
-        for K,V in self.items():
+        items = self.items()
+        items.sort()
+        for K,V in items:
             if V == "": continue
             if K not in attrs: continue
             if K == "expires" and type(V) == type(1):
@@ -586,7 +588,9 @@ class BaseCookie(UserDict):
     def output(self, attrs=None, header="Set-Cookie:", sep="\n"):
         """Return a string suitable for HTTP."""
         result = []
-        for K,V in self.items():
+        items = self.items()
+        items.sort()
+        for K,V in items:
             result.append( V.output(attrs, header) )
         return string.join(result, sep)
     # end output
@@ -595,14 +599,18 @@ class BaseCookie(UserDict):
 
     def __repr__(self):
         L = []
-        for K,V in self.items():
+        items = self.items()
+        items.sort()
+        for K,V in items:
             L.append( '%s=%s' % (K,repr(V.value) ) )
         return '<%s: %s>' % (self.__class__.__name__, string.join(L))
 
     def js_output(self, attrs=None):
         """Return a string suitable for JavaScript."""
         result = []
-        for K,V in self.items():
+        items = self.items()
+        items.sort()
+        for K,V in items:
             result.append( V.js_output(attrs) )
         return string.join(result, "")
     # end js_output

Lib/test/output/test_cookie

 test_cookie
-<SimpleCookie: vienna='finger' chips='ahoy'>
-Set-Cookie: vienna=finger;
+<SimpleCookie: chips='ahoy' vienna='finger'>
 Set-Cookie: chips=ahoy;
-  vienna 'finger' 'finger'
 Set-Cookie: vienna=finger;
   chips 'ahoy' 'ahoy'
 Set-Cookie: chips=ahoy;
+  vienna 'finger' 'finger'
+Set-Cookie: vienna=finger;
 <SimpleCookie: keebler='E=mc2; L="Loves"; fudge=\n;'>
 Set-Cookie: keebler="E=mc2; L=\"Loves\"; fudge=\012;";
   keebler 'E=mc2; L="Loves"; fudge=\n;' 'E=mc2; L="Loves"; fudge=\n;'

Lib/test/output/test_extcall

@@ -40,7 +40,7 @@ za () {} -> za() takes exactly 1 argument (0 given)
 za () {'a': 'aa'} -> ok za aa B D E V a
 za () {'d': 'dd'} -> za() got an unexpected keyword argument 'd'
 za () {'a': 'aa', 'd': 'dd'} -> za() got an unexpected keyword argument 'd'
-za () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> za() got an unexpected keyword argument 'd'
+za () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> za() got an unexpected keyword argument 'b'
 za (1, 2) {} -> za() takes exactly 1 argument (2 given)
 za (1, 2) {'a': 'aa'} -> za() takes exactly 1 non-keyword argument (2 given)
 za (1, 2) {'d': 'dd'} -> za() takes exactly 1 non-keyword argument (2 given)
@@ -59,8 +59,8 @@ zade () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got an unexpected
 zade (1, 2) {} -> ok zade 1 B 2 e V e
 zade (1, 2) {'a': 'aa'} -> zade() got multiple values for keyword argument 'a'
 zade (1, 2) {'d': 'dd'} -> zade() got multiple values for keyword argument 'd'
-zade (1, 2) {'a': 'aa', 'd': 'dd'} -> zade() got multiple values for keyword argument 'd'
-zade (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got multiple values for keyword argument 'd'
+zade (1, 2) {'a': 'aa', 'd': 'dd'} -> zade() got multiple values for keyword argument 'a'
+zade (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got multiple values for keyword argument 'a'
 zade (1, 2, 3, 4, 5) {} -> zade() takes at most 3 arguments (5 given)
 zade (1, 2, 3, 4, 5) {'a': 'aa'} -> zade() takes at most 3 non-keyword arguments (5 given)
 zade (1, 2, 3, 4, 5) {'d': 'dd'} -> zade() takes at most 3 non-keyword arguments (5 given)
@@ -75,7 +75,7 @@ zabk (1, 2) {} -> ok zabk 1 2 D E V {}
 zabk (1, 2) {'a': 'aa'} -> zabk() got multiple values for keyword argument 'a'
 zabk (1, 2) {'d': 'dd'} -> ok zabk 1 2 D E V {'d': 'dd'}
 zabk (1, 2) {'a': 'aa', 'd': 'dd'} -> zabk() got multiple values for keyword argument 'a'
-zabk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabk() got multiple values for keyword argument 'b'
+zabk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabk() got multiple values for keyword argument 'a'
 zabk (1, 2, 3, 4, 5) {} -> zabk() takes exactly 2 arguments (5 given)
 zabk (1, 2, 3, 4, 5) {'a': 'aa'} -> zabk() takes exactly 2 non-keyword arguments (5 given)
 zabk (1, 2, 3, 4, 5) {'d': 'dd'} -> zabk() takes exactly 2 non-keyword arguments (5 given)
@@ -90,12 +90,12 @@ zabdv (1, 2) {} -> ok zabdv 1 2 d E () e
 zabdv (1, 2) {'a': 'aa'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2) {'d': 'dd'} -> ok zabdv 1 2 dd E () d
 zabdv (1, 2) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'a'
-zabdv (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got an unexpected keyword argument 'e'
+zabdv (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2, 3, 4, 5) {} -> ok zabdv 1 2 3 E (4, 5) e
 zabdv (1, 2, 3, 4, 5) {'a': 'aa'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2, 3, 4, 5) {'d': 'dd'} -> zabdv() got multiple values for keyword argument 'd'
-zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'd'
-zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'd'
+zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'a'
+zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'a'
 zabdevk () {} -> zabdevk() takes at least 2 arguments (0 given)
 zabdevk () {'a': 'aa'} -> zabdevk() takes at least 2 non-keyword arguments (1 given)
 zabdevk () {'d': 'dd'} -> zabdevk() takes at least 2 non-keyword arguments (0 given)
@@ -105,9 +105,9 @@ zabdevk (1, 2) {} -> ok zabdevk 1 2 d e () {}
 zabdevk (1, 2) {'a': 'aa'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2) {'d': 'dd'} -> ok zabdevk 1 2 dd e () {}
 zabdevk (1, 2) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'a'
-zabdevk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'b'
+zabdevk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2, 3, 4, 5) {} -> ok zabdevk 1 2 3 4 (5,) {}
 zabdevk (1, 2, 3, 4, 5) {'a': 'aa'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2, 3, 4, 5) {'d': 'dd'} -> zabdevk() got multiple values for keyword argument 'd'
-zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'd'
-zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'd'
+zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'a'
+zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'a'

Lib/test/test_cookie.py

@@ -20,7 +20,9 @@ for data, dict in cases:
     C = Cookie.SimpleCookie() ; C.load(data)
     print repr(C)
     print str(C)
-    for k, v in dict.items():
+    items = dict.items()
+    items.sort()
+    for k, v in items:
         print ' ', k, repr( C[k].value ), repr(v)
         verify(C[k].value == v)
         print C[k]

Lib/test/test_extcall.py

-from test_support import verify, verbose, TestFailed
+from test_support import verify, verbose, TestFailed, sortdict
 from UserList import UserList
 
-def sortdict(d):
-    keys = d.keys()
-    keys.sort()
-    lst = []
-    for k in keys:
-        lst.append("%r: %r" % (k, d[k]))
-    return "{%s}" % ", ".join(lst)
-
 def f(*a, **k):
     print a, sortdict(k)
 
@@ -228,8 +220,9 @@ for args in ['', 'a', 'ab']:
                     lambda x: '%s="%s"' % (x, x), defargs)
                 if vararg: arglist.append('*' + vararg)
                 if kwarg: arglist.append('**' + kwarg)
-                decl = 'def %s(%s): print "ok %s", a, b, d, e, v, k' % (
-                    name, ', '.join(arglist), name)
+                decl = (('def %s(%s): print "ok %s", a, b, d, e, v, ' +
+                         'type(k) is type ("") and k or sortdict(k)')
+                         % (name, ', '.join(arglist), name))
                 exec(decl)
                 func = eval(name)
                 funcs.append(func)

Lib/test/test_pyexpat.py

@@ -5,9 +5,11 @@
 
 from xml.parsers import expat
 
+from test_support import sortdict
+
 class Outputter:
     def StartElementHandler(self, name, attrs):
-        print 'Start element:\n\t', repr(name), attrs
+        print 'Start element:\n\t', repr(name), sortdict(attrs)
 
     def EndElementHandler(self, name):
         print 'End element:\n\t', repr(name)

Lib/test/test_regex.py

-from test_support import verbose
+from test_support import verbose, sortdict
 import warnings
 warnings.filterwarnings("ignore", "the regex module is deprecated",
                         DeprecationWarning, __name__)
@@ -40,7 +40,7 @@ print cre.group('one')
 print cre.group(1, 2)
 print cre.group('one', 'two')
 print 'realpat:', cre.realpat
-print 'groupindex:', cre.groupindex
+print 'groupindex:', sortdict(cre.groupindex)
 
 re = 'world'
 cre = regex.compile(re)

Lib/test/test_support.py

@@ -90,6 +90,14 @@ def verify(condition, reason='test failed'):
     if not condition:
         raise TestFailed(reason)
 
+def sortdict(dict):
+    "Like repr(dict), but in sorted order."
+    items = dict.items()
+    items.sort()
+    reprpairs = ["%r: %r" % pair for pair in items]
+    withcommas = ", ".join(reprpairs)
+    return "{%s}" % withcommas
+
 def check_syntax(statement):
     try:
         compile(statement, '<string>', 'exec')

Lib/test/test_unicode.py

@@ -5,7 +5,7 @@ Written by Marc-Andre Lemburg (mal@lemburg.com).
 (c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
 
 """#"
-from test_support import verify, verbose
+from test_support import verify, verbose, TestFailed
 import sys
 
 def test(method, input, output, *args):
@@ -493,11 +493,14 @@ for encoding in (
     'cp856', 'cp857', 'cp864', 'cp869', 'cp874',
 
     'mac_greek', 'mac_iceland','mac_roman', 'mac_turkish',
-    'cp1006', 'cp875', 'iso8859_8',
+    'cp1006', 'iso8859_8',
 
     ### These have undefined mappings:
     #'cp424',
 
+    ### These fail the round-trip:
+    #'cp875'
+
     ):
     try:
         verify(unicode(s,encoding).encode(encoding) == s)

Misc/NEWS

@@ -23,6 +23,16 @@ Core
   usually for the better, but may also cause numerically unstable
   algorithms to break.
 
+- The implementation of dicts suffers fewer collisions, which has speed
+  benefits.  However, the order in which dict entries appear in dict.keys(),
+  dict.values() and dict.items() may differ from previous releases for a
+  given dict.  Nothing is defined about this order, so no program should
+  rely on it.  Nevertheless, it's easy to write test cases that rely on the
+  order by accident, typically because of printing the str() or repr() of a
+  dict to an "expected results" file.  See Lib/test/test_support.py's new
+  sortdict(dict) function for a simple way to display a dict in sorted
+  order.
+
 - Dictionary objects now support the "in" operator: "x in dict" means
   the same as dict.has_key(x).
 

Objects/dictobject.c

@@ -188,12 +188,7 @@ lookdict(dictobject *mp, PyObject *key, register long hash)
 	/* We must come up with (i, incr) such that 0 <= i < ma_size
 	   and 0 < incr < ma_size and both are a function of hash.
 	   i is the initial table index and incr the initial probe offset. */
-	i = (~hash) & mask;
-	/* We use ~hash instead of hash, as degenerate hash functions, such
-	   as for ints <sigh>, can have lots of leading zeros. It's not
-	   really a performance risk, but better safe than sorry.
-	   12-Dec-00 tim:  so ~hash produces lots of leading ones instead --
-	   what's the gain? */
+	i = hash & mask;
 	ep = &ep0[i];
 	if (ep->me_key == NULL || ep->me_key == key)
 		return ep;
@@ -301,10 +296,7 @@ lookdict_string(dictobject *mp, PyObject *key, register long hash)
 	}
 	/* We must come up with (i, incr) such that 0 <= i < ma_size
 	   and 0 < incr < ma_size and both are a function of hash */
-	i = (~hash) & mask;
-	/* We use ~hash instead of hash, as degenerate hash functions, such
-	   as for ints <sigh>, can have lots of leading zeros. It's not
-	   really a performance risk, but better safe than sorry. */
+	i = hash & mask;
 	ep = &ep0[i];
 	if (ep->me_key == NULL || ep->me_key == key)
 		return ep;