use 'x is None' instead of 'x == None'

The built-in None object is a singleton and it is therefore safe to
compare memory addresses with is. It is also faster, how much depends
on the object being compared. For a simple type like str I get:

            | s = "foo" | s = None
  ----------+-----------+----------
  s == None | 0.25 usec | 0.21 usec
  s is None | 0.17 usec | 0.17 usec

contrib/hgdiff

@@ -37,13 +37,13 b' def buildlist(names, top):'
                 names[os.path.join(l, x)] = (st.st_dev, st.st_ino)
 
 def diff_files(file1, file2):
-    if file1 == None:
+    if file1 is None:
         b = file(file2).read().splitlines(1)
         l1 = "--- %s\n" % (file2)
         l2 = "+++ %s\n" % (file2)
         l3 = "@@ -0,0 +1,%d @@\n" % len(b)
         l = [l1, l2, l3] + ["+" + e for e in b]
-    elif file2 == None:
+    elif file2 is None:
         a = file(file1).read().splitlines(1)
         l1 = "--- %s\n" % (file1)
         l2 = "+++ %s\n" % (file1)

hgext/bookmarks.py

@@ -143,7 +143,7 b' def bookmark(ui, repo, mark=None, rev=No'
         return
 
     if delete:
-        if mark == None:
+        if mark is None:
             raise util.Abort(_("bookmark name required"))
         if mark not in marks:
             raise util.Abort(_("a bookmark of this name does not exist"))
@@ -171,7 +171,7 b' def bookmark(ui, repo, mark=None, rev=No'
         write(repo, marks)
         return
 
-    if mark == None:
+    if mark is None:
         if rev:
             raise util.Abort(_("bookmark name required"))
         if len(marks) == 0:
@@ -243,7 +243,7 b' def reposetup(ui, repo):'
             """Add a revision to the repository and
             move the bookmark"""
             node  = super(bookmark_repo, self).commit(*k, **kw)
-            if node == None:
+            if node is None:
                 return None
             parents = repo.changelog.parents(node)
             if parents[1] == nullid:

hgext/mq.py

@@ -430,7 +430,7 b' class queue:'
         if ret:
             raise util.Abort(_("update returned %d") % ret)
         n = repo.commit(None, ctx.description(), ctx.user(), force=1)
-        if n == None:
+        if n is None:
             raise util.Abort(_("repo commit failed"))
         try:
             ph = mergeq.readheaders(patch)
@@ -603,7 +603,7 b' class queue:'
             n = repo.commit(files, message, ph.user, ph.date, match=match,
                             force=True)
 
-            if n == None:
+            if n is None:
                 raise util.Abort(_("repo commit failed"))
 
             if update_status:
@@ -767,7 +767,7 b' class queue:'
                     msg = msg()
                 commitmsg = msg and msg or ("[mq]: %s" % patchfn)
                 n = repo.commit(commitfiles, commitmsg, user, date, match=match, force=True)
-                if n == None:
+                if n is None:
                     raise util.Abort(_("repo commit failed"))
                 try:
                     self.full_series[insert:insert] = [patchfn]
@@ -860,7 +860,7 b' class queue:'
                     return self.series[0]
             return None
 
-        if patch == None:
+        if patch is None:
             return None
         if patch in self.series:
             return patch
@@ -1422,7 +1422,7 b' class queue:'
                     applied.append(se)
                 else:
                     series.append(file_)
-        if datastart == None:
+        if datastart is None:
             self.ui.warn(_("No saved patch data found\n"))
             return 1
         self.ui.warn(_("restoring status: %s\n") % lines[0])
@@ -1486,7 +1486,7 b' class queue:'
         if len(self.applied) > 0:
             p = self.applied[-1].name
             end = self.find_series(p)
-            if end == None:
+            if end is None:
                 return len(self.full_series)
             return end + 1
         return 0
@@ -2090,7 +2090,7 b' def lastsavename(path):'
         m = namere.match(f)
         if m:
             index = int(m.group(1))
-            if maxindex == None or index > maxindex:
+            if maxindex is None or index > maxindex:
                 maxindex = index
                 maxname = f
     if maxname:

mercurial/archival.py

@@ -44,7 +44,7 b' class tarit:'
             timestamp = None
             if 'timestamp' in kw:
                 timestamp = kw.pop('timestamp')
-            if timestamp == None:
+            if timestamp is None:
                 self.timestamp = time.time()
             else:
                 self.timestamp = timestamp

mercurial/context.py

@@ -444,7 +444,7 b' class filectx(object):'
 
         # prime the ancestor cache for the working directory
         for c in (self, fc2):
-            if c._filerev == None:
+            if c._filerev is None:
                 pl = [(n.path(), n.filenode()) for n in c.parents()]
                 acache[(c._path, None)] = pl
 

mercurial/copies.py

@@ -106,7 +106,7 b' def copies(repo, c1, c2, ca, checkdirs=F'
         return {}, {}
 
     # avoid silly behavior for parent -> working dir
-    if c2.node() == None and c1.node() == repo.dirstate.parents()[0]:
+    if c2.node() is None and c1.node() == repo.dirstate.parents()[0]:
         return repo.dirstate.copies(), {}
 
     limit = _findlimit(repo, c1.rev(), c2.rev())

mercurial/localrepo.py

@@ -107,7 +107,7 b' class localrepository(repo.repository):'
         return dirstate.dirstate(self.opener, self.ui, self.root)
 
     def __getitem__(self, changeid):
-        if changeid == None:
+        if changeid is None:
             return context.workingctx(self)
         return context.changectx(self, changeid)
 
@@ -1209,7 +1209,7 b' class localrepository(repo.repository):'
         fetch = set()
         seen = set()
         seenbranch = set()
-        if base == None:
+        if base is None:
             base = {}
 
         if not heads:
@@ -1341,7 +1341,7 b' class localrepository(repo.repository):'
         or ancestors of these heads, and return a second element which
         contains all remote heads which get new children.
         """
-        if base == None:
+        if base is None:
             base = {}
             self.findincoming(remote, base, heads, force=force)
 

mercurial/patch.py

@@ -452,11 +452,11 b' class hunk:'
         if not m:
             raise PatchError(_("bad hunk #%d") % self.number)
         self.starta, foo, self.lena, self.startb, foo2, self.lenb = m.groups()
-        if self.lena == None:
+        if self.lena is None:
             self.lena = 1
         else:
             self.lena = int(self.lena)
-        if self.lenb == None:
+        if self.lenb is None:
             self.lenb = 1
         else:
             self.lenb = int(self.lenb)
@@ -479,7 +479,7 b' class hunk:'
             raise PatchError(_("bad hunk #%d") % self.number)
         foo, self.starta, foo2, aend, foo3 = m.groups()
         self.starta = int(self.starta)
-        if aend == None:
+        if aend is None:
             aend = self.starta
         self.lena = int(aend) - self.starta
         if self.starta:
@@ -511,7 +511,7 b' class hunk:'
             raise PatchError(_("bad hunk #%d") % self.number)
         foo, self.startb, foo2, bend, foo3 = m.groups()
         self.startb = int(self.startb)
-        if bend == None:
+        if bend is None:
             bend = self.startb
         self.lenb = int(bend) - self.startb
         if self.startb:
@@ -872,7 +872,7 b' def iterhunks(ui, fp, sourcefile=None):'
         if ((sourcefile or state == BFILE) and ((not context and x[0] == '@') or
             ((context is not False) and x.startswith('***************')))):
             try:
-                if context == None and x.startswith('***************'):
+                if context is None and x.startswith('***************'):
                     context = True
                 gpatch = changed.get(bfile)
                 create = afile == '/dev/null' or gpatch and gpatch.op == 'ADD'

mercurial/revlog.py

@@ -175,7 +175,7 b' class lazyparser(object):'
         if lend > len(self.index) - i:
             lend = len(self.index) - i
         for x in xrange(lend):
-            if self.index[i + x] == None:
+            if self.index[i + x] is None:
                 b = data[off : off + self.s]
                 self.index[i + x] = b
                 n = b[ngshaoffset:ngshaoffset + 20]
@@ -231,7 +231,7 b' class lazyparser(object):'
         if self.all:
             return
         all = False
-        if i == None:
+        if i is None:
             blockstart = 0
             blocksize = (65536 / self.s) * self.s
             end = self.datasize
@@ -279,7 +279,7 b' class lazymap(object):'
         self.p = parser
     def load(self, key):
         n = self.p.findnode(key)
-        if n == None:
+        if n is None:
             raise KeyError(key)
     def __contains__(self, key):
         if key in self.p.map:
@@ -1019,7 +1019,7 b' class revlog(object):'
             return
 
         trinfo = tr.find(self.indexfile)
-        if trinfo == None:
+        if trinfo is None:
             raise RevlogError(_("%s not found in the transaction")
                               % self.indexfile)
 

mercurial/ui.py

@@ -129,7 +129,7 b' class ui(object):'
 
     def configbool(self, section, name, default=False, untrusted=False):
         v = self.config(section, name, None, untrusted)
-        if v == None:
+        if v is None:
             return default
         if v.lower() not in _booleans:
             raise error.ConfigError(_("%s.%s not a boolean ('%s')")