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 #   isinstance    -- version of the isinstance() function that accepts
   8 #                    tuples as the second parameter regardless of the
   9 #                    Python version
  10 #
  11 #   NodeList      -- lightest possible NodeList implementation
  12 #
  13 #   EmptyNodeList -- lightest possible NodeList that is guarateed to
  14 #                    remain empty (immutable)
  15 #
  16 #   StringTypes   -- tuple of defined string types
  17 #
  18 #   GetattrMagic  -- base class used to make _get_<attr> be magically
  19 #                    invoked when available
  20 #   defproperty   -- function used in conjunction with GetattrMagic;
  21 #                    using these together is needed to make them work
  22 #                    as efficiently as possible in both Python 2.2+
  23 #                    and older versions.  For example:
  24 #
  25 #                        class MyClass(GetattrMagic):
  26 #                            def _get_myattr(self):
  27 #                                return something
  28 #
  29 #                        defproperty(MyClass, "myattr",
  30 #                                    "return some value")
  31 #
  32 #                    For Python 2.2 and newer, this will construct a
  33 #                    property object on the class, which avoids
  34 #                    needing to override __getattr__().  It will only
  35 #                    work for read-only attributes.
  36 #
  37 #                    For older versions of Python, inheriting from
  38 #                    GetattrMagic will use the traditional
  39 #                    __getattr__() hackery to achieve the same effect,
  40 #                    but less efficiently.
  41 #
  42 #                    defproperty() should be used for each version of
  43 #                    the relevant _get_<property>() function.
  44 #
  45 #   NewStyle      -- base class to cause __slots__ to be honored in
  46 #                    the new world
  47 #
  48 #   True, False   -- only for Python 2.2 and earlier
  49
  50 __all__ = ["NodeList", "EmptyNodeList", "NewStyle",
  51            "StringTypes", "defproperty", "GetattrMagic"]
  52
  53 import xml.dom
  54
  55 try:
  56     unicode
  57 except NameError:
  58     StringTypes = type(''),
  59 else:
  60     StringTypes = type(''), type(unicode(''))
  61
  62
  63 # define True and False only if not defined as built-ins
  64 try:
  65     True
  66 except NameError:
  67     True = 1
  68     False = 0
  69     __all__.extend(["True", "False"])
  70
  71
  72 try:
  73     isinstance('', StringTypes)
  74 except TypeError:
  75     #
  76     # Wrap isinstance() to make it compatible with the version in
  77     # Python 2.2 and newer.
  78     #
  79     _isinstance = isinstance
  80     def isinstance(obj, type_or_seq):
  81         try:
  82             return _isinstance(obj, type_or_seq)
  83         except TypeError:
  84             for t in type_or_seq:
  85                 if _isinstance(obj, t):
  86                     return 1
  87             return 0
  88     __all__.append("isinstance")
  89
  90
  91 if list is type([]):
  92     class NodeList(list):
  93         __slots__ = ()
  94
  95         def item(self, index):
  96             if 0 <= index < len(self):
  97                 return self[index]
  98
  99         def _get_length(self):
 100             return len(self)
 101
 102         def _set_length(self, value):
 103             raise xml.dom.NoModificationAllowedErr(
 104                 "attempt to modify read-only attribute 'length'")
 105
 106         length = property(_get_length, _set_length,
 107                           doc="The number of nodes in the NodeList.")
 108
 109         def __getstate__(self):
 110             return list(self)
 111
 112         def __setstate__(self, state):
 113             self[:] = state
 114
 115     class EmptyNodeList(tuple):
 116         __slots__ = ()
 117
 118         def __add__(self, other):
 119             NL = NodeList()
 120             NL.extend(other)
 121             return NL
 122
 123         def __radd__(self, other):
 124             NL = NodeList()
 125             NL.extend(other)
 126             return NL
 127
 128         def item(self, index):
 129             return None
 130
 131         def _get_length(self):
 132             return 0
 133
 134         def _set_length(self, value):
 135             raise xml.dom.NoModificationAllowedErr(
 136                 "attempt to modify read-only attribute 'length'")
 137
 138         length = property(_get_length, _set_length,
 139                           doc="The number of nodes in the NodeList.")
 140
 141 else:
 142     def NodeList():
 143         return []
 144
 145     def EmptyNodeList():
 146         return []
 147
 148
 149 try:
 150     property
 151 except NameError:
 152     def defproperty(klass, name, doc):
 153         # taken care of by the base __getattr__()
 154         pass
 155
 156     class GetattrMagic:
 157         def __getattr__(self, key):
 158             if key.startswith("_"):
 159                 raise AttributeError, key
 160
 161             try:
 162                 get = getattr(self, "_get_" + key)
 163             except AttributeError:
 164                 raise AttributeError, key
 165             return get()
 166
 167     class NewStyle:
 168         pass
 169
 170 else:
 171     def defproperty(klass, name, doc):
 172         get = getattr(klass, ("_get_" + name)).im_func
 173         def set(self, value, name=name):
 174             raise xml.dom.NoModificationAllowedErr(
 175                 "attempt to modify read-only attribute " + repr(name))
 176         assert not hasattr(klass, "_set_" + name), \
 177                "expected not to find _set_" + name
 178         prop = property(get, set, doc=doc)
 179         setattr(klass, name, prop)
 180
 181     class GetattrMagic:
 182         pass
 183
 184     NewStyle = object