updated from Atlas

03-dict-set/transformdict.py

@@ -0,0 +1,142 @@
+"""Transformdict: a mapping that transforms keys on lookup
+
+This module and ``test_transformdict.py`` were extracted from a
+patch contributed to Python by Antoine Pitrou implementing his
+PEP 455 -- Adding a key-transforming dictionary to collections.
+
+As of Nov. 14, 2014, the patch was not yet merged to Python 3.5
+(which is in pre-alpha). The patch is ``transformdict3.patch``,
+part of issue #18986: Add a case-insensitive case-preserving dict.
+
+http://bugs.python.org/issue18986
+"""
+
+from collections.abc import MutableMapping
+
+
+_sentinel = object()
+
+
+class TransformDict(MutableMapping):
+    '''Dictionary that calls a transformation function when looking
+    up keys, but preserves the original keys.
+
+    >>> d = TransformDict(str.lower)
+    >>> d['Foo'] = 5
+    >>> d['foo'] == d['FOO'] == d['Foo'] == 5
+    True
+    >>> set(d.keys())
+    {'Foo'}
+    '''
+
+    __slots__ = ('_transform', '_original', '_data')
+
+    def __init__(self, transform, init_dict=None, **kwargs):
+        '''Create a new TransformDict with the given *transform* function.
+        *init_dict* and *kwargs* are optional initializers, as in the
+        dict constructor.
+        '''
+        if not callable(transform):
+            msg = 'expected a callable, got %r'
+            raise TypeError(msg % transform.__class__)
+        self._transform = transform
+        # transformed => original
+        self._original = {}
+        self._data = {}
+        if init_dict:
+            self.update(init_dict)
+        if kwargs:
+            self.update(kwargs)
+
+    def getitem(self, key):
+        'D.getitem(key) -> (stored key, value)'
+        transformed = self._transform(key)
+        original = self._original[transformed]
+        value = self._data[transformed]
+        return original, value
+
+    @property
+    def transform_func(self):
+        "This TransformDict's transformation function"
+        return self._transform
+
+    # Minimum set of methods required for MutableMapping
+
+    def __len__(self):
+        return len(self._data)
+
+    def __iter__(self):
+        return iter(self._original.values())
+
+    def __getitem__(self, key):
+        return self._data[self._transform(key)]
+
+    def __setitem__(self, key, value):
+        transformed = self._transform(key)
+        self._data[transformed] = value
+        self._original.setdefault(transformed, key)
+
+    def __delitem__(self, key):
+        transformed = self._transform(key)
+        del self._data[transformed]
+        del self._original[transformed]
+
+    # Methods overridden to mitigate the performance overhead.
+
+    def clear(self):
+        'D.clear() -> None.  Remove all items from D.'
+        self._data.clear()
+        self._original.clear()
+
+    def __contains__(self, key):
+        return self._transform(key) in self._data
+
+    def get(self, key, default=None):
+        'D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None.'
+        return self._data.get(self._transform(key), default)
+
+    def pop(self, key, default=_sentinel):
+        '''D.pop(k[,d]) -> v, remove key and return corresponding value.
+           If key is not found, d is returned if given, otherwise
+           KeyError is raised.
+        '''
+        transformed = self._transform(key)
+        if default is _sentinel:
+            del self._original[transformed]
+            return self._data.pop(transformed)
+        else:
+            self._original.pop(transformed, None)
+            return self._data.pop(transformed, default)
+
+    def popitem(self):
+        '''D.popitem() -> (k, v), remove and return some (key, value) pair
+           as a 2-tuple; but raise KeyError if D is empty.
+        '''
+        transformed, value = self._data.popitem()
+        return self._original.pop(transformed), value
+
+    # Other methods
+
+    def copy(self):
+        'D.copy() -> a shallow copy of D'
+        other = self.__class__(self._transform)
+        other._original = self._original.copy()
+        other._data = self._data.copy()
+        return other
+
+    __copy__ = copy
+
+    def __getstate__(self):
+        return (self._transform, self._data, self._original)
+
+    def __setstate__(self, state):
+        self._transform, self._data, self._original = state
+
+    def __repr__(self):
+        try:
+            equiv = dict(self)
+        except TypeError:
+            # Some keys are unhashable, fall back on .items()
+            equiv = list(self.items())
+        return '%s(%r, %s)' % (self.__class__.__name__,
+                               self._transform, repr(equiv))