Merge commit 'upstream/1.2.0.d20091224'

1 files changed, 1645 insertions, 0 deletions

diff --git a/engine/SCons/Util.py b/engine/SCons/Util.py
new file mode 100644
index 0000000..e1f33c7
--- /dev/null
+++ b/engine/SCons/Util.py
@@ -0,0 +1,1645 @@
+"""SCons.Util
+
+Various utility functions go here.
+
+"""
+
+#
+# Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 The SCons Foundation
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+#
+
+__revision__ = "src/engine/SCons/Util.py 4577 2009/12/27 19:43:56 scons"
+
+import copy
+import os
+import os.path
+import re
+import string
+import sys
+import types
+
+from UserDict import UserDict
+from UserList import UserList
+from UserString import UserString
+
+# Don't "from types import ..." these because we need to get at the
+# types module later to look for UnicodeType.
+DictType        = types.DictType
+InstanceType    = types.InstanceType
+ListType        = types.ListType
+StringType      = types.StringType
+TupleType       = types.TupleType
+
+def dictify(keys, values, result={}):
+    for k, v in zip(keys, values):
+        result[k] = v
+    return result
+
+_altsep = os.altsep
+if _altsep is None and sys.platform == 'win32':
+    # My ActivePython 2.0.1 doesn't set os.altsep!  What gives?
+    _altsep = '/'
+if _altsep:
+    def rightmost_separator(path, sep, _altsep=_altsep):
+        rfind = string.rfind
+        return max(rfind(path, sep), rfind(path, _altsep))
+else:
+    rightmost_separator = string.rfind
+
+# First two from the Python Cookbook, just for completeness.
+# (Yeah, yeah, YAGNI...)
+def containsAny(str, set):
+    """Check whether sequence str contains ANY of the items in set."""
+    for c in set:
+        if c in str: return 1
+    return 0
+
+def containsAll(str, set):
+    """Check whether sequence str contains ALL of the items in set."""
+    for c in set:
+        if c not in str: return 0
+    return 1
+
+def containsOnly(str, set):
+    """Check whether sequence str contains ONLY items in set."""
+    for c in str:
+        if c not in set: return 0
+    return 1
+
+def splitext(path):
+    "Same as os.path.splitext() but faster."
+    sep = rightmost_separator(path, os.sep)
+    dot = string.rfind(path, '.')
+    # An ext is only real if it has at least one non-digit char
+    if dot > sep and not containsOnly(path[dot:], "0123456789."):
+        return path[:dot],path[dot:]
+    else:
+        return path,""
+
+def updrive(path):
+    """
+    Make the drive letter (if any) upper case.
+    This is useful because Windows is inconsitent on the case
+    of the drive letter, which can cause inconsistencies when
+    calculating command signatures.
+    """
+    drive, rest = os.path.splitdrive(path)
+    if drive:
+        path = string.upper(drive) + rest
+    return path
+
+class NodeList(UserList):
+    """This class is almost exactly like a regular list of Nodes
+    (actually it can hold any object), with one important difference.
+    If you try to get an attribute from this list, it will return that
+    attribute from every item in the list.  For example:
+
+    >>> someList = NodeList([ '  foo  ', '  bar  ' ])
+    >>> someList.strip()
+    [ 'foo', 'bar' ]
+    """
+    def __nonzero__(self):
+        return len(self.data) != 0
+
+    def __str__(self):
+        return string.join(map(str, self.data))
+
+    def __iter__(self):
+        return iter(self.data)
+
+    def __call__(self, *args, **kwargs):
+        result = map(lambda x, args=args, kwargs=kwargs: apply(x,
+                                                               args,
+                                                               kwargs),
+                     self.data)
+        return self.__class__(result)
+
+    def __getattr__(self, name):
+        result = map(lambda x, n=name: getattr(x, n), self.data)
+        return self.__class__(result)
+
+
+_get_env_var = re.compile(r'^\$([_a-zA-Z]\w*|{[_a-zA-Z]\w*})$')
+
+def get_environment_var(varstr):
+    """Given a string, first determine if it looks like a reference
+    to a single environment variable, like "$FOO" or "${FOO}".
+    If so, return that variable with no decorations ("FOO").
+    If not, return None."""
+    mo=_get_env_var.match(to_String(varstr))
+    if mo:
+        var = mo.group(1)
+        if var[0] == '{':
+            return var[1:-1]
+        else:
+            return var
+    else:
+        return None
+
+class DisplayEngine:
+    def __init__(self):
+        self.__call__ = self.print_it
+
+    def print_it(self, text, append_newline=1):
+        if append_newline: text = text + '\n'
+        try:
+            sys.stdout.write(text)
+        except IOError:
+            # Stdout might be connected to a pipe that has been closed
+            # by now. The most likely reason for the pipe being closed
+            # is that the user has press ctrl-c. It this is the case,
+            # then SCons is currently shutdown. We therefore ignore
+            # IOError's here so that SCons can continue and shutdown
+            # properly so that the .sconsign is correctly written
+            # before SCons exits.
+            pass
+
+    def dont_print(self, text, append_newline=1):
+        pass
+
+    def set_mode(self, mode):
+        if mode:
+            self.__call__ = self.print_it
+        else:
+            self.__call__ = self.dont_print
+
+def render_tree(root, child_func, prune=0, margin=[0], visited={}):
+    """
+    Render a tree of nodes into an ASCII tree view.
+    root - the root node of the tree
+    child_func - the function called to get the children of a node
+    prune - don't visit the same node twice
+    margin - the format of the left margin to use for children of root.
+       1 results in a pipe, and 0 results in no pipe.
+    visited - a dictionary of visited nodes in the current branch if not prune,
+       or in the whole tree if prune.
+    """
+
+    rname = str(root)
+
+    children = child_func(root)
+    retval = ""
+    for pipe in margin[:-1]:
+        if pipe:
+            retval = retval + "| "
+        else:
+            retval = retval + "  "
+
+    if visited.has_key(rname):
+        return retval + "+-[" + rname + "]\n"
+
+    retval = retval + "+-" + rname + "\n"
+    if not prune:
+        visited = copy.copy(visited)
+    visited[rname] = 1
+
+    for i in range(len(children)):
+        margin.append(i<len(children)-1)
+        retval = retval + render_tree(children[i], child_func, prune, margin, visited
+)
+        margin.pop()
+
+    return retval
+
+IDX = lambda N: N and 1 or 0
+
+def print_tree(root, child_func, prune=0, showtags=0, margin=[0], visited={}):
+    """
+    Print a tree of nodes.  This is like render_tree, except it prints
+    lines directly instead of creating a string representation in memory,
+    so that huge trees can be printed.
+
+    root - the root node of the tree
+    child_func - the function called to get the children of a node
+    prune - don't visit the same node twice
+    showtags - print status information to the left of each node line
+    margin - the format of the left margin to use for children of root.
+       1 results in a pipe, and 0 results in no pipe.
+    visited - a dictionary of visited nodes in the current branch if not prune,
+       or in the whole tree if prune.
+    """
+
+    rname = str(root)
+
+    if showtags:
+
+        if showtags == 2:
+            print ' E         = exists'
+            print '  R        = exists in repository only'
+            print '   b       = implicit builder'
+            print '   B       = explicit builder'
+            print '    S      = side effect'
+            print '     P     = precious'
+            print '      A    = always build'
+            print '       C   = current'
+            print '        N  = no clean'
+            print '         H = no cache'
+            print ''
+
+        tags = ['[']
+        tags.append(' E'[IDX(root.exists())])
+        tags.append(' R'[IDX(root.rexists() and not root.exists())])
+        tags.append(' BbB'[[0,1][IDX(root.has_explicit_builder())] +
+                           [0,2][IDX(root.has_builder())]])
+        tags.append(' S'[IDX(root.side_effect)])
+        tags.append(' P'[IDX(root.precious)])
+        tags.append(' A'[IDX(root.always_build)])
+        tags.append(' C'[IDX(root.is_up_to_date())])
+        tags.append(' N'[IDX(root.noclean)])
+        tags.append(' H'[IDX(root.nocache)])
+        tags.append(']')
+
+    else:
+        tags = []
+
+    def MMM(m):
+        return ["  ","| "][m]
+    margins = map(MMM, margin[:-1])
+
+    children = child_func(root)
+
+    if prune and visited.has_key(rname) and children:
+        print string.join(tags + margins + ['+-[', rname, ']'], '')
+        return
+
+    print string.join(tags + margins + ['+-', rname], '')
+
+    visited[rname] = 1
+
+    if children:
+        margin.append(1)
+        idx = IDX(showtags)
+        for C in children[:-1]:
+            print_tree(C, child_func, prune, idx, margin, visited)
+        margin[-1] = 0
+        print_tree(children[-1], child_func, prune, idx, margin, visited)
+        margin.pop()
+
+
+
+# Functions for deciding if things are like various types, mainly to
+# handle UserDict, UserList and UserString like their underlying types.
+#
+# Yes, all of this manual testing breaks polymorphism, and the real
+# Pythonic way to do all of this would be to just try it and handle the
+# exception, but handling the exception when it's not the right type is
+# often too slow.
+
+try:
+    class mystr(str):
+        pass
+except TypeError:
+    # An older Python version without new-style classes.
+    #
+    # The actual implementations here have been selected after timings
+    # coded up in in bench/is_types.py (from the SCons source tree,
+    # see the scons-src distribution), mostly against Python 1.5.2.
+    # Key results from those timings:
+    #
+    #   --  Storing the type of the object in a variable (t = type(obj))
+    #       slows down the case where it's a native type and the first
+    #       comparison will match, but nicely speeds up the case where
+    #       it's a different native type.  Since that's going to be
+    #       common, it's a good tradeoff.
+    #
+    #   --  The data show that calling isinstance() on an object that's
+    #       a native type (dict, list or string) is expensive enough
+    #       that checking up front for whether the object is of type
+    #       InstanceType is a pretty big win, even though it does slow
+    #       down the case where it really *is* an object instance a
+    #       little bit.
+    def is_Dict(obj):
+        t = type(obj)
+        return t is DictType or \
+               (t is InstanceType and isinstance(obj, UserDict))
+
+    def is_List(obj):
+        t = type(obj)
+        return t is ListType \
+            or (t is InstanceType and isinstance(obj, UserList))
+
+    def is_Sequence(obj):
+        t = type(obj)
+        return t is ListType \
+            or t is TupleType \
+            or (t is InstanceType and isinstance(obj, UserList))
+
+    def is_Tuple(obj):
+        t = type(obj)
+        return t is TupleType
+
+    if hasattr(types, 'UnicodeType'):
+        def is_String(obj):
+            t = type(obj)
+            return t is StringType \
+                or t is UnicodeType \
+                or (t is InstanceType and isinstance(obj, UserString))
+    else:
+        def is_String(obj):
+            t = type(obj)
+            return t is StringType \
+                or (t is InstanceType and isinstance(obj, UserString))
+
+    def is_Scalar(obj):
+        return is_String(obj) or not is_Sequence(obj)
+
+    def flatten(obj, result=None):
+        """Flatten a sequence to a non-nested list.
+
+        Flatten() converts either a single scalar or a nested sequence
+        to a non-nested list. Note that flatten() considers strings
+        to be scalars instead of sequences like Python would.
+        """
+        if is_Scalar(obj):
+            return [obj]
+        if result is None:
+            result = []
+        for item in obj:
+            if is_Scalar(item):
+                result.append(item)
+            else:
+                flatten_sequence(item, result)
+        return result
+
+    def flatten_sequence(sequence, result=None):
+        """Flatten a sequence to a non-nested list.
+
+        Same as flatten(), but it does not handle the single scalar
+        case. This is slightly more efficient when one knows that
+        the sequence to flatten can not be a scalar.
+        """
+        if result is None:
+            result = []
+        for item in sequence:
+            if is_Scalar(item):
+                result.append(item)
+            else:
+                flatten_sequence(item, result)
+        return result
+
+    #
+    # Generic convert-to-string functions that abstract away whether or
+    # not the Python we're executing has Unicode support.  The wrapper
+    # to_String_for_signature() will use a for_signature() method if the
+    # specified object has one.
+    #
+    if hasattr(types, 'UnicodeType'):
+        UnicodeType = types.UnicodeType
+        def to_String(s):
+            if isinstance(s, UserString):
+                t = type(s.data)
+            else:
+                t = type(s)
+            if t is UnicodeType:
+                return unicode(s)
+            else:
+                return str(s)
+    else:
+        to_String = str
+
+    def to_String_for_signature(obj):
+        try:
+            f = obj.for_signature
+        except AttributeError:
+            return to_String_for_subst(obj)
+        else:
+            return f()
+
+    def to_String_for_subst(s):
+        if is_Sequence( s ):
+            return string.join( map(to_String_for_subst, s) )
+
+        return to_String( s )
+
+else:
+    # A modern Python version with new-style classes, so we can just use
+    # isinstance().
+    #
+    # We are using the following trick to speed-up these
+    # functions. Default arguments are used to take a snapshot of the
+    # the global functions and constants used by these functions. This
+    # transforms accesses to global variable into local variables
+    # accesses (i.e. LOAD_FAST instead of LOAD_GLOBAL).
+
+    DictTypes = (dict, UserDict)
+    ListTypes = (list, UserList)
+    SequenceTypes = (list, tuple, UserList)
+
+    # Empirically, Python versions with new-style classes all have
+    # unicode.
+    #
+    # Note that profiling data shows a speed-up when comparing
+    # explicitely with str and unicode instead of simply comparing
+    # with basestring. (at least on Python 2.5.1)
+    StringTypes = (str, unicode, UserString)
+
+    # Empirically, it is faster to check explicitely for str and
+    # unicode than for basestring.
+    BaseStringTypes = (str, unicode)
+
+    def is_Dict(obj, isinstance=isinstance, DictTypes=DictTypes):
+        return isinstance(obj, DictTypes)
+
+    def is_List(obj, isinstance=isinstance, ListTypes=ListTypes):
+        return isinstance(obj, ListTypes)
+
+    def is_Sequence(obj, isinstance=isinstance, SequenceTypes=SequenceTypes):
+        return isinstance(obj, SequenceTypes)
+
+    def is_Tuple(obj, isinstance=isinstance, tuple=tuple):
+        return isinstance(obj, tuple)
+
+    def is_String(obj, isinstance=isinstance, StringTypes=StringTypes):
+        return isinstance(obj, StringTypes)
+
+    def is_Scalar(obj, isinstance=isinstance, StringTypes=StringTypes, SequenceTypes=SequenceTypes):
+        # Profiling shows that there is an impressive speed-up of 2x
+        # when explicitely checking for strings instead of just not
+        # sequence when the argument (i.e. obj) is already a string.
+        # But, if obj is a not string than it is twice as fast to
+        # check only for 'not sequence'. The following code therefore
+        # assumes that the obj argument is a string must of the time.
+        return isinstance(obj, StringTypes) or not isinstance(obj, SequenceTypes)
+
+    def do_flatten(sequence, result, isinstance=isinstance, 
+                   StringTypes=StringTypes, SequenceTypes=SequenceTypes):
+        for item in sequence:
+            if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
+                result.append(item)
+            else:
+                do_flatten(item, result)
+
+    def flatten(obj, isinstance=isinstance, StringTypes=StringTypes, 
+                SequenceTypes=SequenceTypes, do_flatten=do_flatten):
+        """Flatten a sequence to a non-nested list.
+
+        Flatten() converts either a single scalar or a nested sequence
+        to a non-nested list. Note that flatten() considers strings
+        to be scalars instead of sequences like Python would.
+        """
+        if isinstance(obj, StringTypes) or not isinstance(obj, SequenceTypes):
+            return [obj]
+        result = []
+        for item in obj:
+            if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
+                result.append(item)
+            else:
+                do_flatten(item, result)
+        return result
+
+    def flatten_sequence(sequence, isinstance=isinstance, StringTypes=StringTypes, 
+                         SequenceTypes=SequenceTypes, do_flatten=do_flatten):
+        """Flatten a sequence to a non-nested list.
+
+        Same as flatten(), but it does not handle the single scalar
+        case. This is slightly more efficient when one knows that
+        the sequence to flatten can not be a scalar.
+        """
+        result = []
+        for item in sequence:
+            if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
+                result.append(item)
+            else:
+                do_flatten(item, result)
+        return result
+
+
+    #
+    # Generic convert-to-string functions that abstract away whether or
+    # not the Python we're executing has Unicode support.  The wrapper
+    # to_String_for_signature() will use a for_signature() method if the
+    # specified object has one.
+    #
+    def to_String(s, 
+                  isinstance=isinstance, str=str,
+                  UserString=UserString, BaseStringTypes=BaseStringTypes):
+        if isinstance(s,BaseStringTypes):
+            # Early out when already a string!
+            return s
+        elif isinstance(s, UserString):
+            # s.data can only be either a unicode or a regular
+            # string. Please see the UserString initializer.
+            return s.data
+        else:
+            return str(s)
+
+    def to_String_for_subst(s, 
+                            isinstance=isinstance, join=string.join, str=str, to_String=to_String,
+                            BaseStringTypes=BaseStringTypes, SequenceTypes=SequenceTypes,
+                            UserString=UserString):
+                            
+        # Note that the test cases are sorted by order of probability.
+        if isinstance(s, BaseStringTypes):
+            return s
+        elif isinstance(s, SequenceTypes):
+            l = []
+            for e in s:
+                l.append(to_String_for_subst(e))
+            return join( s )
+        elif isinstance(s, UserString):
+            # s.data can only be either a unicode or a regular
+            # string. Please see the UserString initializer.
+            return s.data
+        else:
+            return str(s)
+
+    def to_String_for_signature(obj, to_String_for_subst=to_String_for_subst, 
+                                AttributeError=AttributeError):
+        try:
+            f = obj.for_signature
+        except AttributeError:
+            return to_String_for_subst(obj)
+        else:
+            return f()
+
+
+
+# The SCons "semi-deep" copy.
+#
+# This makes separate copies of lists (including UserList objects)
+# dictionaries (including UserDict objects) and tuples, but just copies
+# references to anything else it finds.
+#
+# A special case is any object that has a __semi_deepcopy__() method,
+# which we invoke to create the copy, which is used by the BuilderDict
+# class because of its extra initialization argument.
+#
+# The dispatch table approach used here is a direct rip-off from the
+# normal Python copy module.
+
+_semi_deepcopy_dispatch = d = {}
+
+def _semi_deepcopy_dict(x):
+    copy = {}
+    for key, val in x.items():
+        # The regular Python copy.deepcopy() also deepcopies the key,
+        # as follows:
+        #
+        #    copy[semi_deepcopy(key)] = semi_deepcopy(val)
+        #
+        # Doesn't seem like we need to, but we'll comment it just in case.
+        copy[key] = semi_deepcopy(val)
+    return copy
+d[types.DictionaryType] = _semi_deepcopy_dict
+
+def _semi_deepcopy_list(x):
+    return map(semi_deepcopy, x)
+d[types.ListType] = _semi_deepcopy_list
+
+def _semi_deepcopy_tuple(x):
+    return tuple(map(semi_deepcopy, x))
+d[types.TupleType] = _semi_deepcopy_tuple
+
+def _semi_deepcopy_inst(x):
+    if hasattr(x, '__semi_deepcopy__'):
+        return x.__semi_deepcopy__()
+    elif isinstance(x, UserDict):
+        return x.__class__(_semi_deepcopy_dict(x))
+    elif isinstance(x, UserList):
+        return x.__class__(_semi_deepcopy_list(x))
+    else:
+        return x
+d[types.InstanceType] = _semi_deepcopy_inst
+
+def semi_deepcopy(x):
+    copier = _semi_deepcopy_dispatch.get(type(x))
+    if copier:
+        return copier(x)
+    else:
+        return x
+
+
+
+class Proxy:
+    """A simple generic Proxy class, forwarding all calls to
+    subject.  So, for the benefit of the python newbie, what does
+    this really mean?  Well, it means that you can take an object, let's
+    call it 'objA', and wrap it in this Proxy class, with a statement
+    like this
+
+                 proxyObj = Proxy(objA),
+
+    Then, if in the future, you do something like this
+
+                 x = proxyObj.var1,
+
+    since Proxy does not have a 'var1' attribute (but presumably objA does),
+    the request actually is equivalent to saying
+
+                 x = objA.var1
+
+    Inherit from this class to create a Proxy."""
+
+    def __init__(self, subject):
+        """Wrap an object as a Proxy object"""
+        self.__subject = subject
+
+    def __getattr__(self, name):
+        """Retrieve an attribute from the wrapped object.  If the named
+           attribute doesn't exist, AttributeError is raised"""
+        return getattr(self.__subject, name)
+
+    def get(self):
+        """Retrieve the entire wrapped object"""
+        return self.__subject
+
+    def __cmp__(self, other):
+        if issubclass(other.__class__, self.__subject.__class__):
+            return cmp(self.__subject, other)
+        return cmp(self.__dict__, other.__dict__)
+
+# attempt to load the windows registry module:
+can_read_reg = 0
+try:
+    import _winreg
+
+    can_read_reg = 1
+    hkey_mod = _winreg
+
+    RegOpenKeyEx    = _winreg.OpenKeyEx
+    RegEnumKey      = _winreg.EnumKey
+    RegEnumValue    = _winreg.EnumValue
+    RegQueryValueEx = _winreg.QueryValueEx
+    RegError        = _winreg.error
+
+except ImportError:
+    try:
+        import win32api
+        import win32con
+        can_read_reg = 1
+        hkey_mod = win32con
+
+        RegOpenKeyEx    = win32api.RegOpenKeyEx
+        RegEnumKey      = win32api.RegEnumKey
+        RegEnumValue    = win32api.RegEnumValue
+        RegQueryValueEx = win32api.RegQueryValueEx
+        RegError        = win32api.error
+
+    except ImportError:
+        class _NoError(Exception):
+            pass
+        RegError = _NoError
+
+if can_read_reg:
+    HKEY_CLASSES_ROOT  = hkey_mod.HKEY_CLASSES_ROOT
+    HKEY_LOCAL_MACHINE = hkey_mod.HKEY_LOCAL_MACHINE
+    HKEY_CURRENT_USER  = hkey_mod.HKEY_CURRENT_USER
+    HKEY_USERS         = hkey_mod.HKEY_USERS
+
+    def RegGetValue(root, key):
+        """This utility function returns a value in the registry
+        without having to open the key first.  Only available on
+        Windows platforms with a version of Python that can read the
+        registry.  Returns the same thing as
+        SCons.Util.RegQueryValueEx, except you just specify the entire
+        path to the value, and don't have to bother opening the key
+        first.  So:
+
+        Instead of:
+          k = SCons.Util.RegOpenKeyEx(SCons.Util.HKEY_LOCAL_MACHINE,
+                r'SOFTWARE\Microsoft\Windows\CurrentVersion')
+          out = SCons.Util.RegQueryValueEx(k,
+                'ProgramFilesDir')
+
+        You can write:
+          out = SCons.Util.RegGetValue(SCons.Util.HKEY_LOCAL_MACHINE,
+                r'SOFTWARE\Microsoft\Windows\CurrentVersion\ProgramFilesDir')
+        """
+        # I would use os.path.split here, but it's not a filesystem
+        # path...
+        p = key.rfind('\\') + 1
+        keyp = key[:p-1]          # -1 to omit trailing slash
+        val = key[p:]
+        k = RegOpenKeyEx(root, keyp)
+        return RegQueryValueEx(k,val)
+else:
+    try:
+        e = WindowsError
+    except NameError:
+        # Make sure we have a definition of WindowsError so we can
+        # run platform-independent tests of Windows functionality on
+        # platforms other than Windows.  (WindowsError is, in fact, an
+        # OSError subclass on Windows.)
+        class WindowsError(OSError):
+            pass
+        import __builtin__
+        __builtin__.WindowsError = WindowsError
+    else:
+        del e
+        
+    HKEY_CLASSES_ROOT = None
+    HKEY_LOCAL_MACHINE = None
+    HKEY_CURRENT_USER = None
+    HKEY_USERS = None
+
+    def RegGetValue(root, key):
+        raise WindowsError
+
+    def RegOpenKeyEx(root, key):
+        raise WindowsError
+
+if sys.platform == 'win32':
+
+    def WhereIs(file, path=None, pathext=None, reject=[]):
+        if path is None:
+            try:
+                path = os.environ['PATH']
+            except KeyError:
+                return None
+        if is_String(path):
+            path = string.split(path, os.pathsep)
+        if pathext is None:
+            try:
+                pathext = os.environ['PATHEXT']
+            except KeyError:
+                pathext = '.COM;.EXE;.BAT;.CMD'
+        if is_String(pathext):
+            pathext = string.split(pathext, os.pathsep)
+        for ext in pathext:
+            if string.lower(ext) == string.lower(file[-len(ext):]):
+                pathext = ['']
+                break
+        if not is_List(reject) and not is_Tuple(reject):
+            reject = [reject]
+        for dir in path:
+            f = os.path.join(dir, file)
+            for ext in pathext:
+                fext = f + ext
+                if os.path.isfile(fext):
+                    try:
+                        reject.index(fext)
+                    except ValueError:
+                        return os.path.normpath(fext)
+                    continue
+        return None
+
+elif os.name == 'os2':
+
+    def WhereIs(file, path=None, pathext=None, reject=[]):
+        if path is None:
+            try:
+                path = os.environ['PATH']
+            except KeyError:
+                return None
+        if is_String(path):
+            path = string.split(path, os.pathsep)
+        if pathext is None:
+            pathext = ['.exe', '.cmd']
+        for ext in pathext:
+            if string.lower(ext) == string.lower(file[-len(ext):]):
+                pathext = ['']
+                break
+        if not is_List(reject) and not is_Tuple(reject):
+            reject = [reject]
+        for dir in path:
+            f = os.path.join(dir, file)
+            for ext in pathext:
+                fext = f + ext
+                if os.path.isfile(fext):
+                    try:
+                        reject.index(fext)
+                    except ValueError:
+                        return os.path.normpath(fext)
+                    continue
+        return None
+
+else:
+
+    def WhereIs(file, path=None, pathext=None, reject=[]):
+        import stat
+        if path is None:
+            try:
+                path = os.environ['PATH']
+            except KeyError:
+                return None
+        if is_String(path):
+            path = string.split(path, os.pathsep)
+        if not is_List(reject) and not is_Tuple(reject):
+            reject = [reject]
+        for d in path:
+            f = os.path.join(d, file)
+            if os.path.isfile(f):
+                try:
+                    st = os.stat(f)
+                except OSError:
+                    # os.stat() raises OSError, not IOError if the file
+                    # doesn't exist, so in this case we let IOError get
+                    # raised so as to not mask possibly serious disk or
+                    # network issues.
+                    continue
+                if stat.S_IMODE(st[stat.ST_MODE]) & 0111:
+                    try:
+                        reject.index(f)
+                    except ValueError:
+                        return os.path.normpath(f)
+                    continue
+        return None
+
+def PrependPath(oldpath, newpath, sep = os.pathsep, 
+                delete_existing=1, canonicalize=None):
+    """This prepends newpath elements to the given oldpath.  Will only
+    add any particular path once (leaving the first one it encounters
+    and ignoring the rest, to preserve path order), and will
+    os.path.normpath and os.path.normcase all paths to help assure
+    this.  This can also handle the case where the given old path
+    variable is a list instead of a string, in which case a list will
+    be returned instead of a string.
+
+    Example:
+      Old Path: "/foo/bar:/foo"
+      New Path: "/biz/boom:/foo"
+      Result:   "/biz/boom:/foo:/foo/bar"
+
+    If delete_existing is 0, then adding a path that exists will
+    not move it to the beginning; it will stay where it is in the
+    list.
+
+    If canonicalize is not None, it is applied to each element of 
+    newpath before use.
+    """
+
+    orig = oldpath
+    is_list = 1
+    paths = orig
+    if not is_List(orig) and not is_Tuple(orig):
+        paths = string.split(paths, sep)
+        is_list = 0
+
+    if is_String(newpath):
+        newpaths = string.split(newpath, sep)
+    elif not is_List(newpath) and not is_Tuple(newpath):
+        newpaths = [ newpath ]  # might be a Dir
+    else:
+        newpaths = newpath
+
+    if canonicalize:
+        newpaths=map(canonicalize, newpaths)
+
+    if not delete_existing:
+        # First uniquify the old paths, making sure to 
+        # preserve the first instance (in Unix/Linux,
+        # the first one wins), and remembering them in normpaths.
+        # Then insert the new paths at the head of the list
+        # if they're not already in the normpaths list.
+        result = []
+        normpaths = []
+        for path in paths:
+            if not path:
+                continue
+            normpath = os.path.normpath(os.path.normcase(path))
+            if normpath not in normpaths:
+                result.append(path)
+                normpaths.append(normpath)
+        newpaths.reverse()      # since we're inserting at the head
+        for path in newpaths:
+            if not path:
+                continue
+            normpath = os.path.normpath(os.path.normcase(path))
+            if normpath not in normpaths:
+                result.insert(0, path)
+                normpaths.append(normpath)
+        paths = result
+
+    else:
+        newpaths = newpaths + paths # prepend new paths
+
+        normpaths = []
+        paths = []
+        # now we add them only if they are unique
+        for path in newpaths:
+            normpath = os.path.normpath(os.path.normcase(path))
+            if path and not normpath in normpaths:
+                paths.append(path)
+                normpaths.append(normpath)
+
+    if is_list:
+        return paths
+    else:
+        return string.join(paths, sep)
+
+def AppendPath(oldpath, newpath, sep = os.pathsep, 
+               delete_existing=1, canonicalize=None):
+    """This appends new path elements to the given old path.  Will
+    only add any particular path once (leaving the last one it
+    encounters and ignoring the rest, to preserve path order), and
+    will os.path.normpath and os.path.normcase all paths to help
+    assure this.  This can also handle the case where the given old
+    path variable is a list instead of a string, in which case a list
+    will be returned instead of a string.
+
+    Example:
+      Old Path: "/foo/bar:/foo"
+      New Path: "/biz/boom:/foo"
+      Result:   "/foo/bar:/biz/boom:/foo"
+
+    If delete_existing is 0, then adding a path that exists
+    will not move it to the end; it will stay where it is in the list.
+
+    If canonicalize is not None, it is applied to each element of 
+    newpath before use.
+    """
+
+    orig = oldpath
+    is_list = 1
+    paths = orig
+    if not is_List(orig) and not is_Tuple(orig):
+        paths = string.split(paths, sep)
+        is_list = 0
+
+    if is_String(newpath):
+        newpaths = string.split(newpath, sep)
+    elif not is_List(newpath) and not is_Tuple(newpath):
+        newpaths = [ newpath ]  # might be a Dir
+    else:
+        newpaths = newpath
+
+    if canonicalize:
+        newpaths=map(canonicalize, newpaths)
+
+    if not delete_existing:
+        # add old paths to result, then
+        # add new paths if not already present
+        # (I thought about using a dict for normpaths for speed,
+        # but it's not clear hashing the strings would be faster
+        # than linear searching these typically short lists.)
+        result = []
+        normpaths = []
+        for path in paths:
+            if not path:
+                continue
+            result.append(path)
+            normpaths.append(os.path.normpath(os.path.normcase(path)))
+        for path in newpaths:
+            if not path:
+                continue
+            normpath = os.path.normpath(os.path.normcase(path))
+            if normpath not in normpaths:
+                result.append(path)
+                normpaths.append(normpath)
+        paths = result
+    else:
+        # start w/ new paths, add old ones if not present,
+        # then reverse.
+        newpaths = paths + newpaths # append new paths
+        newpaths.reverse()
+
+        normpaths = []
+        paths = []
+        # now we add them only if they are unique
+        for path in newpaths:
+            normpath = os.path.normpath(os.path.normcase(path))
+            if path and not normpath in normpaths:
+                paths.append(path)
+                normpaths.append(normpath)
+        paths.reverse()
+
+    if is_list:
+        return paths
+    else:
+        return string.join(paths, sep)
+
+if sys.platform == 'cygwin':
+    def get_native_path(path):
+        """Transforms an absolute path into a native path for the system.  In
+        Cygwin, this converts from a Cygwin path to a Windows one."""
+        return string.replace(os.popen('cygpath -w ' + path).read(), '\n', '')
+else:
+    def get_native_path(path):
+        """Transforms an absolute path into a native path for the system.
+        Non-Cygwin version, just leave the path alone."""
+        return path
+
+display = DisplayEngine()
+
+def Split(arg):
+    if is_List(arg) or is_Tuple(arg):
+        return arg
+    elif is_String(arg):
+        return string.split(arg)
+    else:
+        return [arg]
+
+class CLVar(UserList):
+    """A class for command-line construction variables.
+
+    This is a list that uses Split() to split an initial string along
+    white-space arguments, and similarly to split any strings that get
+    added.  This allows us to Do the Right Thing with Append() and
+    Prepend() (as well as straight Python foo = env['VAR'] + 'arg1
+    arg2') regardless of whether a user adds a list or a string to a
+    command-line construction variable.
+    """
+    def __init__(self, seq = []):
+        UserList.__init__(self, Split(seq))
+    def __add__(self, other):
+        return UserList.__add__(self, CLVar(other))
+    def __radd__(self, other):
+        return UserList.__radd__(self, CLVar(other))
+    def __coerce__(self, other):
+        return (self, CLVar(other))
+    def __str__(self):
+        return string.join(self.data)
+
+# A dictionary that preserves the order in which items are added.
+# Submitted by David Benjamin to ActiveState's Python Cookbook web site:
+#     http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/107747
+# Including fixes/enhancements from the follow-on discussions.
+class OrderedDict(UserDict):
+    def __init__(self, dict = None):
+        self._keys = []
+        UserDict.__init__(self, dict)
+
+    def __delitem__(self, key):
+        UserDict.__delitem__(self, key)
+        self._keys.remove(key)
+
+    def __setitem__(self, key, item):
+        UserDict.__setitem__(self, key, item)
+        if key not in self._keys: self._keys.append(key)
+
+    def clear(self):
+        UserDict.clear(self)
+        self._keys = []
+
+    def copy(self):
+        dict = OrderedDict()
+        dict.update(self)
+        return dict
+
+    def items(self):
+        return zip(self._keys, self.values())
+
+    def keys(self):
+        return self._keys[:]
+
+    def popitem(self):
+        try:
+            key = self._keys[-1]
+        except IndexError:
+            raise KeyError('dictionary is empty')
+
+        val = self[key]
+        del self[key]
+
+        return (key, val)
+
+    def setdefault(self, key, failobj = None):
+        UserDict.setdefault(self, key, failobj)
+        if key not in self._keys: self._keys.append(key)
+
+    def update(self, dict):
+        for (key, val) in dict.items():
+            self.__setitem__(key, val)
+
+    def values(self):
+        return map(self.get, self._keys)
+
+class Selector(OrderedDict):
+    """A callable ordered dictionary that maps file suffixes to
+    dictionary values.  We preserve the order in which items are added
+    so that get_suffix() calls always return the first suffix added."""
+    def __call__(self, env, source, ext=None):
+        if ext is None:
+            try:
+                ext = source[0].suffix
+            except IndexError:
+                ext = ""
+        try:
+            return self[ext]
+        except KeyError:
+            # Try to perform Environment substitution on the keys of
+            # the dictionary before giving up.
+            s_dict = {}
+            for (k,v) in self.items():
+                if k is not None:
+                    s_k = env.subst(k)
+                    if s_dict.has_key(s_k):
+                        # We only raise an error when variables point
+                        # to the same suffix.  If one suffix is literal
+                        # and a variable suffix contains this literal,
+                        # the literal wins and we don't raise an error.
+                        raise KeyError, (s_dict[s_k][0], k, s_k)
+                    s_dict[s_k] = (k,v)
+            try:
+                return s_dict[ext][1]
+            except KeyError:
+                try:
+                    return self[None]
+                except KeyError:
+                    return None
+
+
+if sys.platform == 'cygwin':
+    # On Cygwin, os.path.normcase() lies, so just report back the
+    # fact that the underlying Windows OS is case-insensitive.
+    def case_sensitive_suffixes(s1, s2):
+        return 0
+else:
+    def case_sensitive_suffixes(s1, s2):
+        return (os.path.normcase(s1) != os.path.normcase(s2))
+
+def adjustixes(fname, pre, suf, ensure_suffix=False):
+    if pre:
+        path, fn = os.path.split(os.path.normpath(fname))
+        if fn[:len(pre)] != pre:
+            fname = os.path.join(path, pre + fn)
+    # Only append a suffix if the suffix we're going to add isn't already
+    # there, and if either we've been asked to ensure the specific suffix
+    # is present or there's no suffix on it at all.
+    if suf and fname[-len(suf):] != suf and \
+       (ensure_suffix or not splitext(fname)[1]):
+            fname = fname + suf
+    return fname
+
+
+
+# From Tim Peters,
+# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560
+# ASPN: Python Cookbook: Remove duplicates from a sequence
+# (Also in the printed Python Cookbook.)
+
+def unique(s):
+    """Return a list of the elements in s, but without duplicates.
+
+    For example, unique([1,2,3,1,2,3]) is some permutation of [1,2,3],
+    unique("abcabc") some permutation of ["a", "b", "c"], and
+    unique(([1, 2], [2, 3], [1, 2])) some permutation of
+    [[2, 3], [1, 2]].
+
+    For best speed, all sequence elements should be hashable.  Then
+    unique() will usually work in linear time.
+
+    If not possible, the sequence elements should enjoy a total
+    ordering, and if list(s).sort() doesn't raise TypeError it's
+    assumed that they do enjoy a total ordering.  Then unique() will
+    usually work in O(N*log2(N)) time.
+
+    If that's not possible either, the sequence elements must support
+    equality-testing.  Then unique() will usually work in quadratic
+    time.
+    """
+
+    n = len(s)
+    if n == 0:
+        return []
+
+    # Try using a dict first, as that's the fastest and will usually
+    # work.  If it doesn't work, it will usually fail quickly, so it
+    # usually doesn't cost much to *try* it.  It requires that all the
+    # sequence elements be hashable, and support equality comparison.
+    u = {}
+    try:
+        for x in s:
+            u[x] = 1
+    except TypeError:
+        pass    # move on to the next method
+    else:
+        return u.keys()
+    del u
+
+    # We can't hash all the elements.  Second fastest is to sort,
+    # which brings the equal elements together; then duplicates are
+    # easy to weed out in a single pass.
+    # NOTE:  Python's list.sort() was designed to be efficient in the
+    # presence of many duplicate elements.  This isn't true of all
+    # sort functions in all languages or libraries, so this approach
+    # is more effective in Python than it may be elsewhere.
+    try:
+        t = list(s)
+        t.sort()
+    except TypeError:
+        pass    # move on to the next method
+    else:
+        assert n > 0
+        last = t[0]
+        lasti = i = 1
+        while i < n:
+            if t[i] != last:
+                t[lasti] = last = t[i]
+                lasti = lasti + 1
+            i = i + 1
+        return t[:lasti]
+    del t
+
+    # Brute force is all that's left.
+    u = []
+    for x in s:
+        if x not in u:
+            u.append(x)
+    return u
+
+
+
+# From Alex Martelli,
+# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560
+# ASPN: Python Cookbook: Remove duplicates from a sequence
+# First comment, dated 2001/10/13.
+# (Also in the printed Python Cookbook.)
+
+def uniquer(seq, idfun=None):
+    if idfun is None:
+        def idfun(x): return x
+    seen = {}
+    result = []
+    for item in seq:
+        marker = idfun(item)
+        # in old Python versions:
+        # if seen.has_key(marker)
+        # but in new ones:
+        if marker in seen: continue
+        seen[marker] = 1
+        result.append(item)
+    return result
+
+# A more efficient implementation of Alex's uniquer(), this avoids the
+# idfun() argument and function-call overhead by assuming that all
+# items in the sequence are hashable.
+
+def uniquer_hashables(seq):
+    seen = {}
+    result = []
+    for item in seq:
+        #if not item in seen:
+        if not seen.has_key(item):
+            seen[item] = 1
+            result.append(item)
+    return result
+
+
+
+# Much of the logic here was originally based on recipe 4.9 from the
+# Python CookBook, but we had to dumb it way down for Python 1.5.2.
+class LogicalLines:
+
+    def __init__(self, fileobj):
+        self.fileobj = fileobj
+
+    def readline(self):
+        result = []
+        while 1:
+            line = self.fileobj.readline()
+            if not line:
+                break
+            if line[-2:] == '\\\n':
+                result.append(line[:-2])
+            else:
+                result.append(line)
+                break
+        return string.join(result, '')
+
+    def readlines(self):
+        result = []
+        while 1:
+            line = self.readline()
+            if not line:
+                break
+            result.append(line)
+        return result
+
+
+
+class UniqueList(UserList):
+    def __init__(self, seq = []):
+        UserList.__init__(self, seq)
+        self.unique = True
+    def __make_unique(self):
+        if not self.unique:
+            self.data = uniquer_hashables(self.data)
+            self.unique = True
+    def __lt__(self, other):
+        self.__make_unique()
+        return UserList.__lt__(self, other)
+    def __le__(self, other):
+        self.__make_unique()
+        return UserList.__le__(self, other)
+    def __eq__(self, other):
+        self.__make_unique()
+        return UserList.__eq__(self, other)
+    def __ne__(self, other):
+        self.__make_unique()
+        return UserList.__ne__(self, other)
+    def __gt__(self, other):
+        self.__make_unique()
+        return UserList.__gt__(self, other)
+    def __ge__(self, other):
+        self.__make_unique()
+        return UserList.__ge__(self, other)
+    def __cmp__(self, other):
+        self.__make_unique()
+        return UserList.__cmp__(self, other)
+    def __len__(self):
+        self.__make_unique()
+        return UserList.__len__(self)
+    def __getitem__(self, i):
+        self.__make_unique()
+        return UserList.__getitem__(self, i)
+    def __setitem__(self, i, item):
+        UserList.__setitem__(self, i, item)
+        self.unique = False
+    def __getslice__(self, i, j):
+        self.__make_unique()
+        return UserList.__getslice__(self, i, j)
+    def __setslice__(self, i, j, other):
+        UserList.__setslice__(self, i, j, other)
+        self.unique = False
+    def __add__(self, other):
+        result = UserList.__add__(self, other)
+        result.unique = False
+        return result
+    def __radd__(self, other):
+        result = UserList.__radd__(self, other)
+        result.unique = False
+        return result
+    def __iadd__(self, other):
+        result = UserList.__iadd__(self, other)
+        result.unique = False
+        return result
+    def __mul__(self, other):
+        result = UserList.__mul__(self, other)
+        result.unique = False
+        return result
+    def __rmul__(self, other):
+        result = UserList.__rmul__(self, other)
+        result.unique = False
+        return result
+    def __imul__(self, other):
+        result = UserList.__imul__(self, other)
+        result.unique = False
+        return result
+    def append(self, item):
+        UserList.append(self, item)
+        self.unique = False
+    def insert(self, i):
+        UserList.insert(self, i)
+        self.unique = False
+    def count(self, item):
+        self.__make_unique()
+        return UserList.count(self, item)
+    def index(self, item):
+        self.__make_unique()
+        return UserList.index(self, item)
+    def reverse(self):
+        self.__make_unique()
+        UserList.reverse(self)
+    def sort(self, *args, **kwds):
+        self.__make_unique()
+        #return UserList.sort(self, *args, **kwds)
+        return apply(UserList.sort, (self,)+args, kwds)
+    def extend(self, other):
+        UserList.extend(self, other)
+        self.unique = False
+
+
+
+class Unbuffered:
+    """
+    A proxy class that wraps a file object, flushing after every write,
+    and delegating everything else to the wrapped object.
+    """
+    def __init__(self, file):
+        self.file = file
+    def write(self, arg):
+        try:
+            self.file.write(arg)
+            self.file.flush()
+        except IOError:
+            # Stdout might be connected to a pipe that has been closed
+            # by now. The most likely reason for the pipe being closed
+            # is that the user has press ctrl-c. It this is the case,
+            # then SCons is currently shutdown. We therefore ignore
+            # IOError's here so that SCons can continue and shutdown
+            # properly so that the .sconsign is correctly written
+            # before SCons exits.
+            pass
+    def __getattr__(self, attr):
+        return getattr(self.file, attr)
+
+def make_path_relative(path):
+    """ makes an absolute path name to a relative pathname.
+    """
+    if os.path.isabs(path):
+        drive_s,path = os.path.splitdrive(path)
+
+        import re
+        if not drive_s:
+            path=re.compile("/*(.*)").findall(path)[0]
+        else:
+            path=path[1:]
+
+    assert( not os.path.isabs( path ) ), path
+    return path
+
+
+
+# The original idea for AddMethod() and RenameFunction() come from the
+# following post to the ActiveState Python Cookbook:
+#
+#	ASPN: Python Cookbook : Install bound methods in an instance
+#	http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/223613
+#
+# That code was a little fragile, though, so the following changes
+# have been wrung on it:
+#
+# * Switched the installmethod() "object" and "function" arguments,
+#   so the order reflects that the left-hand side is the thing being
+#   "assigned to" and the right-hand side is the value being assigned.
+#
+# * Changed explicit type-checking to the "try: klass = object.__class__"
+#   block in installmethod() below so that it still works with the
+#   old-style classes that SCons uses.
+#
+# * Replaced the by-hand creation of methods and functions with use of
+#   the "new" module, as alluded to in Alex Martelli's response to the
+#   following Cookbook post:
+#
+#	ASPN: Python Cookbook : Dynamically added methods to a class
+#	http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/81732
+
+def AddMethod(object, function, name = None):
+    """
+    Adds either a bound method to an instance or an unbound method to
+    a class. If name is ommited the name of the specified function
+    is used by default.
+    Example:
+      a = A()
+      def f(self, x, y):
+        self.z = x + y
+      AddMethod(f, A, "add")
+      a.add(2, 4)
+      print a.z
+      AddMethod(lambda self, i: self.l[i], a, "listIndex")
+      print a.listIndex(5)
+    """
+    import new
+
+    if name is None:
+        name = function.func_name
+    else:
+        function = RenameFunction(function, name)
+
+    try:
+        klass = object.__class__
+    except AttributeError:
+        # "object" is really a class, so it gets an unbound method.
+        object.__dict__[name] = new.instancemethod(function, None, object)
+    else:
+        # "object" is really an instance, so it gets a bound method.
+        object.__dict__[name] = new.instancemethod(function, object, klass)
+
+def RenameFunction(function, name):
+    """
+    Returns a function identical to the specified function, but with
+    the specified name.
+    """
+    import new
+
+    # Compatibility for Python 1.5 and 2.1.  Can be removed in favor of
+    # passing function.func_defaults directly to new.function() once
+    # we base on Python 2.2 or later.
+    func_defaults = function.func_defaults
+    if func_defaults is None:
+        func_defaults = ()
+
+    return new.function(function.func_code,
+                        function.func_globals,
+                        name,
+                        func_defaults)
+
+
+md5 = False
+def MD5signature(s):
+    return str(s)
+
+def MD5filesignature(fname, chunksize=65536):
+    f = open(fname, "rb")
+    result = f.read()
+    f.close()
+    return result
+
+try:
+    import hashlib
+except ImportError:
+    pass
+else:
+    if hasattr(hashlib, 'md5'):
+        md5 = True
+        def MD5signature(s):
+            m = hashlib.md5()
+            m.update(str(s))
+            return m.hexdigest()
+
+        def MD5filesignature(fname, chunksize=65536):
+            m = hashlib.md5()
+            f = open(fname, "rb")
+            while 1:
+                blck = f.read(chunksize)
+                if not blck:
+                    break
+                m.update(str(blck))
+            f.close()
+            return m.hexdigest()
+            
+def MD5collect(signatures):
+    """
+    Collects a list of signatures into an aggregate signature.
+
+    signatures - a list of signatures
+    returns - the aggregate signature
+    """
+    if len(signatures) == 1:
+        return signatures[0]
+    else:
+        return MD5signature(string.join(signatures, ', '))
+
+
+
+# Wrap the intern() function so it doesn't throw exceptions if ineligible
+# arguments are passed. The intern() function was moved into the sys module in
+# Python 3.
+try:
+    intern
+except NameError:
+    from sys import intern
+
+def silent_intern(x):
+    """
+    Perform intern() on the passed argument and return the result.
+    If the input is ineligible (e.g. a unicode string) the original argument is
+    returned and no exception is thrown.
+    """
+    try:
+        return intern(x)
+    except TypeError:
+        return x
+
+
+
+# From Dinu C. Gherman,
+# Python Cookbook, second edition, recipe 6.17, p. 277.
+# Also:
+# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/68205
+# ASPN: Python Cookbook: Null Object Design Pattern
+
+# TODO(1.5):
+#class Null(object):
+class Null:
+    """ Null objects always and reliably "do nothing." """
+    def __new__(cls, *args, **kwargs):
+        if not '_inst' in vars(cls):
+            #cls._inst = type.__new__(cls, *args, **kwargs)
+            cls._inst = apply(type.__new__, (cls,) + args, kwargs)
+        return cls._inst
+    def __init__(self, *args, **kwargs):
+        pass
+    def __call__(self, *args, **kwargs):
+        return self
+    def __repr__(self):
+        return "Null(0x%08X)" % id(self)
+    def __nonzero__(self):
+        return False
+    def __getattr__(self, name):
+        return self
+    def __setattr__(self, name, value):
+        return self
+    def __delattr__(self, name):
+        return self
+
+class NullSeq(Null):
+    def __len__(self):
+        return 0
+    def __iter__(self):
+        return iter(())
+    def __getitem__(self, i):
+        return self
+    def __delitem__(self, i):
+        return self
+    def __setitem__(self, i, v):
+        return self
+
+
+del __revision__
+
+# Local Variables:
+# tab-width:4
+# indent-tabs-mode:nil
+# End:
+# vim: set expandtab tabstop=4 shiftwidth=4: