iframe-proxy | Sunbelt Computer Software

142 lines (111 loc) · 4.39 KB
"""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
    >>> 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))
Sunbelt Computer Software

PL/B Language Development and Support

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

transformdict.py

Latest commit

History

transformdict.py

File metadata and controls
