Lib/xml/dom/minicompat.py

   1 """Python version compatibility support for minidom."""
   2
   3 # This module should only be imported using "import *".
   4 #
   5 # The following names are defined:
   6 #
   7 #   NodeList      -- lightest possible NodeList implementation
   8 #
   9 #   EmptyNodeList -- lightest possible NodeList that is guarateed to
  10 #                    remain empty (immutable)
  11 #
  12 #   StringTypes   -- tuple of defined string types
  13 #
  14 #   defproperty   -- function used in conjunction with GetattrMagic;
  15 #                    using these together is needed to make them work
  16 #                    as efficiently as possible in both Python 2.2+
  17 #                    and older versions.  For example:
  18 #
  19 #                        class MyClass(GetattrMagic):
  20 #                            def _get_myattr(self):
  21 #                                return something
  22 #
  23 #                        defproperty(MyClass, "myattr",
  24 #                                    "return some value")
  25 #
  26 #                    For Python 2.2 and newer, this will construct a
  27 #                    property object on the class, which avoids
  28 #                    needing to override __getattr__().  It will only
  29 #                    work for read-only attributes.
  30 #
  31 #                    For older versions of Python, inheriting from
  32 #                    GetattrMagic will use the traditional
  33 #                    __getattr__() hackery to achieve the same effect,
  34 #                    but less efficiently.
  35 #
  36 #                    defproperty() should be used for each version of
  37 #                    the relevant _get_<property>() function.
  38
  39 __all__ = ["NodeList", "EmptyNodeList", "StringTypes", "defproperty"]
  40
  41 import xml.dom
  42
  43 try:
  44     unicode
  45 except NameError:
  46     StringTypes = type(''),
  47 else:
  48     StringTypes = type(''), type(unicode(''))
  49
  50
  51 class NodeList(list):
  52     __slots__ = ()
  53
  54     def item(self, index):
  55         if 0 <= index < len(self):
  56             return self[index]
  57
  58     def _get_length(self):
  59         return len(self)
  60
  61     def _set_length(self, value):
  62         raise xml.dom.NoModificationAllowedErr(
  63             "attempt to modify read-only attribute 'length'")
  64
  65     length = property(_get_length, _set_length,
  66                       doc="The number of nodes in the NodeList.")
  67
  68     def __getstate__(self):
  69         return list(self)
  70
  71     def __setstate__(self, state):
  72         self[:] = state
  73
  74
  75 class EmptyNodeList(tuple):
  76     __slots__ = ()
  77
  78     def __add__(self, other):
  79         NL = NodeList()
  80         NL.extend(other)
  81         return NL
  82
  83     def __radd__(self, other):
  84         NL = NodeList()
  85         NL.extend(other)
  86         return NL
  87
  88     def item(self, index):
  89         return None
  90
  91     def _get_length(self):
  92         return 0
  93
  94     def _set_length(self, value):
  95         raise xml.dom.NoModificationAllowedErr(
  96             "attempt to modify read-only attribute 'length'")
  97
  98     length = property(_get_length, _set_length,
  99                       doc="The number of nodes in the NodeList.")
 100
 101
 102 def defproperty(klass, name, doc):
 103     get = getattr(klass, ("_get_" + name)).im_func
 104     def set(self, value, name=name):
 105         raise xml.dom.NoModificationAllowedErr(
 106             "attempt to modify read-only attribute " + repr(name))
 107     assert not hasattr(klass, "_set_" + name), \
 108            "expected not to find _set_" + name
 109     prop = property(get, set, doc=doc)
 110     setattr(klass, name, prop)