Metadata-Version: 2.1
Name: immutable-views
Version: 0.6.1
Summary: Immutable views on other collection objects
Home-page: https://github.com/andy-maier/immutable-views
Author: Andreas Maier
Author-email: andreas.r.maier@gmx.de
Maintainer: Andreas Maier
Maintainer-email: andreas.r.maier@gmx.de
License: Apache Software License 2.0
Project-URL: Bug Tracker, https://github.com/andy-maier/immutable-views/issues
Project-URL: Documentation, https://immutable-views.readthedocs.io/en/stable/
Project-URL: Change Log, https://immutable-views.readthedocs.io/en/stable/changes.html
Description: immutable-views - Immutable views on other collection objects
        =============================================================
        
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        Overview
        --------
        
        The **immutable-views** package provides collection classes that are immutable
        views on other (mutable) collection objects:
        
        * `DictView <https://immutable-views.readthedocs.io/en/latest/api_dict_view.html>`_ -
          immutable view on another mapping (dictionary) object.
        * `ListView <https://immutable-views.readthedocs.io/en/latest/api_list_view.html>`_ -
          immutable view on another sequence (list) object.
        * `SetView <https://immutable-views.readthedocs.io/en/latest/api_set_view.html>`_ -
          immutable view on another set object.
        
        An important behavior of views is that they are "live": Since the view classes
        delegate to the underlying collection, any modification of the underlying
        collection object will be visible in the view object.
        
        Creating an immutable view on a collection does not copy the collection and
        is therefore much faster than creating an immutable copy of the collection.
        
        The memory overhead of using immutable views is very small: An object
        of any of the view classes in the **immutable-views** package occupies 40 Bytes
        (measured in CPython 3.9 on macOS), and because the view object only has a
        reference to its underlying collection object, that size is independent of the
        number of items in the collection.
        
        The compute overhead is also very small, it is basically an additional function
        call to the corresponding function of the underlying collection.
        
        Immutable views are useful if a method or function maintains data in form of a
        mutable collection and is intended to return that data but users should not be
        able to modify the data. The underlying collection can be updated by the method
        or function as needed, but the caller only gets an immutable view on it.
        
        The view classes in the **immutable-views** package implement the complete
        behavior of the corresponding Python collection types except for any
        operations that would modify the underlying collection object.
        
        The view classes delegate all operations to the underlying collection object
        they are a view of. Therefore, the underlying collection can be any kind of
        collection implementation (i.e. not just the standard Python collection
        classes).
        
        Note that the immutability of the view objects only applies to the view object
        itself and to its underlying collection, but not to the items in the underlying
        collection. So if the underlying collection contains mutable objects, they will
        still be mutable when accessed through the view objects.
        
        The standard Python class
        `types.MappingProxyType <https://docs.python.org/3/library/types.html#types.MappingProxyType>`_
        serves the same purpose as the
        `DictView <https://immutable-views.readthedocs.io/en/latest/api_dict_view.html>`_
        class but it does not support pickling or hashing and was added only in
        Python 3.3.
        The ``dictproxy`` class from the
        `dictproxyhack <https://pypi.org/project/dictproxyhack/>`_
        package on Pypi supports Python 2 and Python 3 and uses Python classes where
        available (e.g. ``MappingProxyType`` on Python 3.3 and later, and the internal
        ``mappingproxy`` class used for ``__dict__`` on CPython) but also does not
        support pickling or hashing.
        The lack of support for standard dictionary behaviors prevents their use in
        cases where the view class is used as a read-only replacement for the standard
        dictionary.
        
        Note that there are several packages on Pypi that provide immutable
        collections, but they all are collections on their own, and not views on
        other collections. Here is a notable subset of such packages:
        
        * `immutables <https://pypi.org/project/immutables/>`_
        * `pyimmutable <https://pypi.org/project/pyimmutable/>`_
        * `frozenordereddict <https://pypi.org/project/frozenordereddict/>`_
        * `immutabledict <https://pypi.org/project/immutabledict/>`_
        * `frozendict <https://pypi.org/project/immutabledict/>`_
        * `itypes <https://pypi.org/project/itypes/>`_
        * `HashableDict <https://pypi.org/project/HashableDict/>`_
        * `shoobx.immutable <https://pypi.org/project/shoobx.immutable/>`_
        * `immutable-collection <https://pypi.org/project/immutable-collection/>`_
        * `Dict-Path-Immutable <https://pypi.org/project/Dict-Path-Immutable/>`_
        
        
        .. _`Examples`:
        
        Examples
        --------
        
        Example with dictionaries:
        
        .. code-block:: bash
        
            $ python
            >>> from immutable_views import DictView
            >>> dict1 = {'a': 1, 'b': 2}
            >>> dictview1 = DictView(dict1)
        
            # Read-only access to the underlying collection through the view is supported:
            >>> dictview1['a']
            1
        
            # Modifying the underlying collection through the view is rejected:
            >>> dictview1['a'] = 2
            Traceback (most recent call last):
              File "<stdin>", line 1, in <module>
            TypeError: 'DictView' object does not support item assignment
        
            # Modifications of the underlying collection are visible in the view:
            >>> dict1['a'] = 2
            >>> dictview1['a']
            2
        
        Example with lists:
        
        .. code-block:: bash
        
            $ python
            >>> from immutable_views import ListView
            >>> list1 = ['a', 'b']
            >>> listview1 = ListView(list1)
        
            # Read-only access to the underlying collection through the view is supported:
            >>> listview1[0]
            'a'
        
            # Modifying the underlying collection through the view is rejected:
            >>> listview1[0] = 'c'
            Traceback (most recent call last):
              File "<stdin>", line 1, in <module>
            TypeError: 'ListView' object does not support item assignment
        
            # Modifications of the underlying collection are visible in the view:
            >>> list1[0] = 'c'
            >>> listview1[0]
            'c'
        
        Example with sets:
        
        .. code-block:: bash
        
            $ python
            >>> from immutable_views import SetView
            >>> set1 = {'a', 'b'}
            >>> setview1 = SetView(set1)
        
            # Read-only access to the underlying collection through the view is supported:
            >>> 'a' in setview1
            True
        
            # Modifying the underlying collection through the view is rejected:
            >>> setview1.add('c')
            Traceback (most recent call last):
              File "<stdin>", line 1, in <module>
            AttributeError: 'SetView' object has no attribute 'add'
        
            # Modifications of the underlying collection are visible in the view:
            >>> set1.add('c')
            >>> 'c' in setview1
            True
        
        
        Documentation and change log
        ----------------------------
        
        * `Documentation <https://immutable-views.readthedocs.io/en/latest/>`_
        * `Change log <https://immutable-views.readthedocs.io/en/latest/changes.html>`_
        
        
        License
        -------
        
        The **immutable-views** project is provided under the
        `Apache Software License 2.0 <https://raw.githubusercontent.com/andy-maier/immutable-views/master/LICENSE>`_.
        
Platform: any
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: Apache Software License
Classifier: Operating System :: OS Independent
Classifier: Programming Language :: Python :: 2
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.4
Classifier: Programming Language :: Python :: 3.5
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Classifier: Programming Language :: Python :: 3.8
Classifier: Programming Language :: Python :: 3.9
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Requires-Python: >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*
Description-Content-Type: text/x-rst
