1. Akis Kesoglou
  2. django-rules

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django-rules ^^^^^^^^^^^^ ``rules`` is a tiny but powerful app providing object-level permissions to Django, without requiring a database. At its core, it is a generic framework for building rule-based systems, similar to `decision trees`_. It can also be used as a standalone library in other contexts and frameworks. .. image:: https://travis-ci.org/dfunckt/django-rules.svg?branch=master :target: https://travis-ci.org/dfunckt/django-rules .. image:: https://coveralls.io/repos/dfunckt/django-rules/badge.svg :target: https://coveralls.io/r/dfunckt/django-rules .. image:: https://img.shields.io/pypi/v/rules.svg :target: https://pypi.python.org/pypi/rules .. image:: https://img.shields.io/pypi/pyversions/rules.svg :target: https://pypi.python.org/pypi/rules .. _decision trees: http://wikipedia.org/wiki/Decision_tree Features ======== ``rules`` has got you covered. ``rules`` is: - **Documented**, **tested**, **reliable** and **easy to use**. - **Versatile**. Decorate callables to build complex graphs of predicates. Predicates can be any type of callable -- simple functions, lambdas, methods, callable class objects, partial functions, decorated functions, anything really. - **A good Django citizen**. Seamless integration with Django views, templates and the Admin for testing for object-level permissions. - **Efficient** and **smart**. No need to mess around with a database to figure out whether John really wrote that book. - **Simple**. Dive in the code. You'll need 10 minutes to figure out how it works. - **Powerful**. ``rules`` comes complete with advanced features, such as invocation context and storage for arbitrary data, skipping evaluation of predicates under specific conditions, logging of evaluated predicates and more! Table of Contents ================= - `Requirements`_ - `How to install`_ - `Configuring Django`_ - `Using Rules`_ - `Creating predicates`_ - `Setting up rules`_ - `Combining predicates`_ - `Using Rules with Django`_ - `Permissions`_ - `Rules and permissions in views`_ - `Rules and permissions in templates`_ - `Rules and permissions in the Admin`_ - `Advanced features`_ - `Custom rule sets`_ - `Invocation context`_ - `Binding "self"`_ - `Skipping predicates`_ - `Logging predicate evaluation`_ - `Best practices`_ - `API Reference`_ - `Changelog`_ - `Licence`_ Requirements ============ ``rules`` requires Python 2.6/3.3 or newer. It can optionally integrate with Django, in which case requires Django 1.5 or newer. How to install ============== Using pip: .. code:: bash $ pip install rules Manually: .. code:: bash $ git clone https://github.com/dfunckt/django-rules.git $ cd django-rules $ python setup.py install Run tests with: .. code:: bash $ ./runtests.sh You may also want to read `Best practices`_ for general advice on how to use ``rules``. Configuring Django ------------------ Add ``rules`` to ``INSTALLED_APPS``: .. code:: python INSTALLED_APPS = ( # ... 'rules', ) Add the authentication backend: .. code:: python AUTHENTICATION_BACKENDS = ( 'rules.permissions.ObjectPermissionBackend', 'django.contrib.auth.backends.ModelBackend', ) Using Rules =========== ``rules`` is based on the idea that you maintain a dict-like object that maps string keys used as identifiers of some kind, to callables, called *predicates*. This dict-like object is actually an instance of ``RuleSet`` and the predicates are instances of ``Predicate``. Creating predicates ------------------- Let's ignore rule sets for a moment and go ahead and define a predicate. The easiest way is with the ``@predicate`` decorator: .. code:: python >>> @rules.predicate >>> def is_book_author(user, book): ... return book.author == user ... >>> is_book_author <Predicate:is_book_author object at 0x10eeaa490> This predicate will return ``True`` if the book's author is the given user, ``False`` otherwise. Predicates can be created from any callable that accepts anything from zero to two positional arguments: * ``fn(obj, target)`` * ``fn(obj)`` * ``fn()`` This is their generic form. If seen from the perspective of authorization in Django, the equivalent signatures are: * ``fn(user, obj)`` * ``fn(user)`` * ``fn()`` Predicates can do pretty much anything with the given arguments, but must always return ``True`` if the condition they check is true, ``False`` otherwise. ``rules`` comes with several predefined predicates that you may read about later on in `API Reference`_, that are mostly useful when dealing with `authorization in Django`_. Setting up rules ---------------- Let's pretend that we want to let authors edit or delete their books, but not books written by other authors. So, essentially, what determines whether an author *can edit* or *can delete* a given book is *whether they are its author*. In ``rules``, such requirements are modelled as *rules*. A *rule* is a map of a unique identifier (eg. "can edit") to a predicate. Rules are grouped together into a *rule set*. ``rules`` has two predefined rule sets: * A default rule set storing shared rules. * Another rule set storing rules that serve as permissions in a Django context. So, let's define our first couple of rules, adding them to the shared rule set. We can use the ``is_book_author`` predicate we defined earlier: .. code:: python >>> rules.add_rule('can_edit_book', is_book_author) >>> rules.add_rule('can_delete_book', is_book_author) Assuming we've got some data, we can now test our rules: .. code:: python >>> from django.contrib.auth.models import User >>> from books.models import Book >>> guidetodjango = Book.objects.get(isbn='978-1-4302-1936-1') >>> guidetodjango.author <User: adrian> >>> adrian = User.objects.get(username='adrian') >>> rules.test_rule('can_edit_book', adrian, guidetodjango) True >>> rules.test_rule('can_delete_book', adrian, guidetodjango) True Nice... but not awesome. Combining predicates -------------------- Predicates by themselves are not so useful -- not more useful than any other function would be. Predicates, however, can be combined using binary operators to create more complex ones. Predicates support the following operators: * ``P1 & P2``: Returns a new predicate that returns ``True`` if *both* predicates return ``True``, otherwise ``False``. If P1 returns ``False``, P2 will not be evaluated. * ``P1 | P2``: Returns a new predicate that returns ``True`` if *any* of the predicates returns ``True``, otherwise ``False``. If P1 returns ``True``, P2 will not be evaluated. * ``P1 ^ P2``: Returns a new predicate that returns ``True`` if one of the predicates returns ``True`` and the other returns ``False``, otherwise ``False``. * ``~P``: Returns a new predicate that returns the negated result of the original predicate. Suppose the requirement for allowing a user to edit a given book was for them to be either the book's author, or a member of the "editors" group. Allowing users to delete a book should still be determined by whether the user is the book's author. With ``rules`` that's easy to implement. We'd have to define another predicate, that would return ``True`` if the given user is a member of the "editors" group, ``False`` otherwise. The built-in ``is_group_member`` factory will come in handy: .. code:: python >>> is_editor = rules.is_group_member('editors') >>> is_editor <Predicate:is_group_member:editors object at 0x10eee1350> We could combine it with the ``is_book_author`` predicate to create a new one that checks for either condition: .. code:: python >>> is_book_author_or_editor = is_book_author | is_editor >>> is_book_author_or_editor <Predicate:(is_book_author | is_group_member:editors) object at 0x10eee1390> We can now update our ``can_edit_book`` rule: .. code:: python >>> rules.add_rule('can_edit_book', is_book_author_or_editor) Traceback (most recent call last): ... KeyError: A rule with name `can_edit_book` already exists >>> rules.remove_rule('can_edit_book') >>> rules.add_rule('can_edit_book', is_book_author_or_editor) >>> rules.test_rule('can_edit_book', adrian, guidetodjango) True >>> rules.test_rule('can_delete_book', adrian, guidetodjango) True Let's see what happens with another user: .. code:: python >>> martin = User.objects.get(username='martin') >>> list(martin.groups.values_list('name', flat=True)) ['editors'] >>> rules.test_rule('can_edit_book', martin, guidetodjango) True >>> rules.test_rule('can_delete_book', martin, guidetodjango) False Awesome. So far, we've only used the underlying, generic framework for defining and testing rules. This layer is not at all specific to Django; it may be used in any context. There's actually no import of anything Django-related in the whole app (except in the ``rules.templatetags`` module). ``rules`` however can integrate tightly with Django to provide authorization. .. _authorization in Django: Using Rules with Django ======================= ``rules`` is able to provide object-level permissions in Django. It comes with an authorization backend and a couple template tags for use in your templates. Permissions ----------- In ``rules``, permissions are a specialised type of rules. You still define rules by creating and combining predicates. These rules however, must be added to a permissions-specific rule set that comes with ``rules`` so that they can be picked up by the ``rules`` authorization backend. Creating permissions ++++++++++++++++++++ The convention for naming permissions in Django is ``app_label.action_object``, and we like to adhere to that. Let's add rules for the ``books.change_book`` and ``books.delete_book`` permissions: .. code:: python >>> rules.add_perm('books.change_book', is_book_author | is_editor) >>> rules.add_perm('books.delete_book', is_book_author) See the difference in the API? ``add_perm`` adds to a permissions-specific rule set, whereas ``add_rule`` adds to a default shared rule set. It's important to know however, that these two rule sets are separate, meaning that adding a rule in one does not make it available to the other. Checking for permission +++++++++++++++++++++++ Let's go ahead and check whether ``adrian`` has change permission to the ``guidetodjango`` book: .. code:: python >>> adrian.has_perm('books.change_book', guidetodjango) False When you call the ``User.has_perm`` method, Django asks each backend in ``settings.AUTHENTICATION_BACKENDS`` whether a user has the given permission for the object. When queried for object permissions, Django's default authentication backend always returns ``False``. ``rules`` comes with an authorization backend, that is able to provide object-level permissions by looking into the permissions-specific rule set. Let's add the ``rules`` authorization backend in settings: .. code:: python AUTHENTICATION_BACKENDS = ( 'rules.permissions.ObjectPermissionBackend', 'django.contrib.auth.backends.ModelBackend', ) Now, checking again gives ``adrian`` the required permissions: .. code:: python >>> adrian.has_perm('books.change_book', guidetodjango) True >>> adrian.has_perm('books.delete_book', guidetodjango) True >>> martin.has_perm('books.change_book', guidetodjango) True >>> martin.has_perm('books.delete_book', guidetodjango) False Rules and permissions in views ------------------------------ ``rules`` comes with a set of view decorators to help you enforce authorization in your views. Using the function-based view decorator +++++++++++++++++++++++++++++++++++++++ For function-based views you can use the ``permission_required`` decorator: .. code:: python from django.shortcuts import get_object_or_404 from rules.contrib.views import permission_required from posts.models import Post def get_post_by_pk(request, post_id): return get_object_or_404(Post, pk=post_id) @permission_required('posts.change_post', fn=get_post_by_pk) def post_update(request, post_id): # ... Usage is straight-forward, but there's one thing in the example above that stands out and this is the ``get_post_by_pk`` function. This function, given the current request and all arguments passed to the view, is responsible for fetching and returning the object to check permissions against -- i.e. the ``Post`` instance with PK equal to the given ``post_id`` in the example. This specific use-case is quite common so, to save you some typing, ``rules`` comes with a generic helper function that you can use to do this declaratively. The example below is equivalent to the one above: .. code:: python from rules.contrib.views import permission_required, objectgetter from posts.models import Post @permission_required('posts.change_post', fn=objectgetter(Post, 'post_id')) def post_update(request, post_id): # ... For more information on the decorator and helper function, refer to the ``rules.contrib.views`` module. Using the class-based view mixin ++++++++++++++++++++++++++++++++ Django 1.9 introduced a new set of access mixins that you can use in your class-based views to enforce authorization. ``rules`` extends this framework to provide a mixin for object-level permissions, ``PermissionRequiredMixin``. Note that ``rules`` will seamlessly fall back to importing its own copy of Django's access mixins module for versions of Django prior to 1.9. The following example will automatically test for permission against the instance returned by the view's ``get_object`` method: .. code:: python from django.views.generic.edit import UpdateView from rules.contrib.views import PermissionRequiredMixin from posts.models import Post class PostUpdate(PermissionRequiredMixin, UpdateView): model = Post permission_required = 'posts.change_post' You can customise the object either by overriding ``get_object`` or ``get_permission_object``. For more information refer to the `Django documentation`_ and the ``rules.contrib.views`` module. .. _Django documentation: https://docs.djangoproject.com/en/1.9/topics/auth/default/#limiting-access-to-logged-in-users Rules and permissions in templates ---------------------------------- ``rules`` comes with two template tags to allow you to test for rules and permissions in templates. Add ``rules`` to your ``INSTALLED_APPS``: .. code:: python INSTALLED_APPS = ( # ... 'rules', ) Then, in your template:: {% load rules %} {% has_perm 'books.change_book' author book as can_edit_book %} {% if can_edit_book %} ... {% endif %} {% test_rule 'has_super_feature' user as has_super_feature %} {% if has_super_feature %} ... {% endif %} Rules and permissions in the Admin ---------------------------------- If you've setup ``rules`` to be used with permissions in Django, you're almost set to also use ``rules`` to authorize any add/change/delete actions in the Admin. The Admin asks for *four* different permissions, depending on action: - ``<app_label>.add_<modelname>`` - ``<app_label>.change_<modelname>`` - ``<app_label>.delete_<modelname>`` - ``<app_label>`` The first three are obvious. The fourth is the required permission for an app to be displayed in the Admin's "dashboard". Here's some rules for our imaginary ``books`` app as an example: .. code:: python >>> rules.add_perm('books', rules.always_allow) >>> rules.add_perm('books.add_book', is_staff) >>> rules.add_perm('books.change_book', is_staff) >>> rules.add_perm('books.delete_book', is_staff) Django Admin does not support object-permissions, in the sense that it will never ask for permission to perform an action *on an object*, only whether a user is allowed to act on (*any*) instances of a model. If you'd like to tell Django whether a user has permissions on a specific object, you'd have to override the following methods of a model's ``ModelAdmin``: - ``has_change_permission(user, obj=None)`` - ``has_delete_permission(user, obj=None)`` **Note:** There's also ``has_add_permission(user)`` but is not relevant here. ``rules`` comes with a custom ``ModelAdmin`` subclass, ``rules.contrib.admin.ObjectPermissionsModelAdmin``, that overrides these methods to pass on the edited model instance to the authorization backends, thus enabling permissions per object in the Admin: .. code:: python # books/admin.py from django.contrib import admin from rules.contrib.admin import ObjectPermissionsModelAdmin from .models import Book class BookAdmin(ObjectPermissionsModelAdmin): pass admin.site.register(Book, BookAdmin) Now this allows you to specify permissions like this: .. code:: python >>> rules.add_perm('books', rules.always_allow) >>> rules.add_perm('books.add_book', has_author_profile) >>> rules.add_perm('books.change_book', is_book_author_or_editor) >>> rules.add_perm('books.delete_book', is_book_author) Advanced features ================= Custom rule sets ---------------- You may create as many rule sets as you need: .. code:: python >>> features = rules.RuleSet() And manipulate them by adding, removing, querying and testing rules: .. code:: python >>> features.rule_exists('has_super_feature') False >>> is_special_user = rules.is_group_member('special') >>> features.add_rule('has_super_feature', is_special_user) >>> 'has_super_feature' in features True >>> features['has_super_feature'] <Predicate:is_group_member:special object at 0x10eeaa500> >>> features.test_rule('has_super_feature', adrian) True >>> features.remove_rule('has_super_feature') Note however that custom rule sets are *not available* in Django templates -- you need to provide integration yourself. Invocation context ------------------ A new context is created as a result of invoking ``Predicate.test()`` and is only valid for the duration of the invocation. A context is a simple ``dict`` that you can use to store arbitrary data, (eg. caching computed values, setting flags, etc.), that can be used by predicates later on in the chain. Inside a predicate function it can be used like so: .. code:: python >>> @predicate ... def mypred(a, b): ... value = compute_expensive_value(a) ... mypred.context['value'] = value ... return True Other predicates can later use stored values: .. code:: python >>> @predicate ... def myotherpred(a, b): ... value = myotherpred.context.get('value') ... if value is not None: ... return do_something_with_value(value) ... else: ... return do_something_without_value() ``Predicate.context`` provides a single ``args`` attribute that contains the arguments as given to ``test()`` at the beginning of the invocation. Binding "self" -------------- In a predicate's function body, you can refer to the predicate instance itself by its name, eg. ``is_book_author``. Passing ``bind=True`` as a keyword argument to the ``predicate`` decorator will let you refer to the predicate with ``self``, which is more convenient. Binding ``self`` is just syntactic sugar. As a matter of fact, the following two are equivalent: .. code:: python >>> @predicate ... def is_book_author(user, book): ... if is_book_author.context.args: ... return user == book.author ... return False >>> @predicate(bind=True) ... def is_book_author(self, user, book): ... if self.context.args: ... return user == book.author ... return False Skipping predicates ------------------- You may skip evaluation by returning ``None`` from your predicate: .. code:: python >>> @predicate(bind=True) ... def is_book_author(self, user, book): ... if len(self.context.args) > 1: ... return user == book.author ... else: ... return None Returning ``None`` signifies that the predicate need not be evaluated, thus leaving the predicate result up to that point unchanged. **Note:** This is new in version 1.1.0. It was possible to skip predicates in older versions by calling the predicate's ``skip()`` method, but this has been deprecated and support will be completely removed in a future version. Logging predicate evaluation ---------------------------- ``rules`` can optionally be configured to log debug information as rules are evaluated to help with debugging your predicates. Messages are sent at the DEBUG level to the ``'rules'`` logger. The following `dictConfig`_ configures a console logger (place this in your project's `settings.py` if you're using `rules` with Django): .. code:: python LOGGING = { 'version': 1, 'disable_existing_loggers': False, 'handlers': { 'console': { 'level': 'DEBUG', 'class': 'logging.StreamHandler', }, }, 'loggers': { 'rules': { 'handlers': ['console'], 'level': 'DEBUG', 'propagate': True, }, }, } When this logger is active each individual predicate will have a log message printed when it is evaluated. .. _dictConfig: https://docs.python.org/3.6/library/logging.config.html#logging-config-dictschema Best practices ============== Before you can test for rules, these rules must be registered with a rule set, and for this to happen the modules containing your rule definitions must be imported. For complex projects with several predicates and rules, it may not be practical to define all your predicates and rules inside one module. It might be best to split them among any sub-components of your project. In a Django context, these sub-components could be the apps for your project. On the other hand, because importing predicates from all over the place in order to define rules can lead to circular imports and broken hearts, it's best to further split predicates and rules in different modules. If using Django 1.7 and later, ``rules`` may optionally be configured to autodiscover ``rules.py`` modules in your apps and import them at startup. To have ``rules`` do so, just edit your ``INSTALLED_APPS`` setting: .. code:: python INSTALLED_APPS = ( # replace 'rules' with: 'rules.apps.AutodiscoverRulesConfig', ) **Note:** On Python 2, you must also add the following to the top of your ``rules.py`` file, or you'll get import errors trying to import ``django-rules`` itself: .. code:: python from __future__ import absolute_import API Reference ============= Everything is accessible from the root ``rules`` module. Class ``rules.Predicate`` ------------------------- You create ``Predicate`` instances by passing in a callable: .. code:: python >>> def is_book_author(user, book): ... return book.author == user ... >>> pred = Predicate(is_book_author) >>> pred <Predicate:is_book_author object at 0x10eeaa490> You may optionally provide a different name for the predicate that is used when inspecting it: .. code:: python >>> pred = Predicate(is_book_author, name='another_name') >>> pred <Predicate:another_name object at 0x10eeaa490> Also, you may optionally provide ``bind=True`` in order to be able to access the predicate instance with ``self``: .. code:: python >>> def is_book_author(self, user, book): ... if self.context.args: ... return user == book.author ... return False ... >>> pred = Predicate(is_book_author, bind=True) >>> pred <Predicate:is_book_author object at 0x10eeaa490> Instance methods ++++++++++++++++ ``test(obj=None, target=None)`` Returns the result of calling the passed in callable with zero, one or two positional arguments, depending on how many it accepts. Class ``rules.RuleSet`` ----------------------- ``RuleSet`` extends Python's built-in `dict`_ type. Therefore, you may create and use a rule set any way you'd use a dict. .. _dict: http://docs.python.org/library/stdtypes.html#mapping-types-dict Instance methods ++++++++++++++++ ``add_rule(name, predicate)`` Adds a predicate to the rule set, assigning it to the given rule name. Raises ``KeyError`` if another rule with that name already exists. ``remove_rule(name)`` Remove the rule with the given name. Raises ``KeyError`` if a rule with that name does not exist. ``rule_exists(name)`` Returns ``True`` if a rule with the given name exists, ``False`` otherwise. ``test_rule(name, obj=None, target=None)`` Returns the result of calling ``predicate.test(obj, target)`` where ``predicate`` is the predicate for the rule with the given name. Returns ``False`` if a rule with the given name does not exist. Decorators ---------- ``@predicate`` Decorator that creates a predicate out of any callable: .. code:: python >>> @predicate ... def is_book_author(user, book): ... return book.author == user ... >>> is_book_author <Predicate:is_book_author object at 0x10eeaa490> Customising the predicate name: .. code:: python >>> @predicate(name='another_name') ... def is_book_author(user, book): ... return book.author == user ... >>> is_book_author <Predicate:another_name object at 0x10eeaa490> Binding ``self``: .. code:: python >>> @predicate(bind=True) ... def is_book_author(self, user, book): ... if 'user_has_special_flag' in self.context: ... return self.context['user_has_special_flag'] ... return book.author == user Predefined predicates --------------------- ``always_allow()``, ``always_true()`` Always returns ``True``. ``always_deny()``, ``always_false()`` Always returns ``False``. ``is_authenticated(user)`` Returns the result of calling ``user.is_authenticated()``. Returns ``False`` if the given user does not have an ``is_authenticated`` method. ``is_superuser(user)`` Returns the result of calling ``user.is_superuser``. Returns ``False`` if the given user does not have an ``is_superuser`` property. ``is_staff(user)`` Returns the result of calling ``user.is_staff``. Returns ``False`` if the given user does not have an ``is_staff`` property. ``is_active(user)`` Returns the result of calling ``user.is_active``. Returns ``False`` if the given user does not have an ``is_active`` property. ``is_group_member(*groups)`` Factory that creates a new predicate that returns ``True`` if the given user is a member of *all* the given groups, ``False`` otherwise. Shortcuts --------- Managing the shared rule set ++++++++++++++++++++++++++++ ``add_rule(name, predicate)`` Adds a rule to the shared rule set. See ``RuleSet.add_rule``. ``remove_rule(name)`` Remove a rule from the shared rule set. See ``RuleSet.remove_rule``. ``rule_exists(name)`` Returns whether a rule exists in the shared rule set. See ``RuleSet.rule_exists``. ``test_rule(name, obj=None, target=None)`` Tests the rule with the given name. See ``RuleSet.test_rule``. Managing the permissions rule set +++++++++++++++++++++++++++++++++ ``add_perm(name, predicate)`` Adds a rule to the permissions rule set. See ``RuleSet.add_rule``. ``remove_perm(name)`` Remove a rule from the permissions rule set. See ``RuleSet.remove_rule``. ``perm_exists(name)`` Returns whether a rule exists in the permissions rule set. See ``RuleSet.rule_exists``. ``has_perm(name, user=None, obj=None)`` Tests the rule with the given name. See ``RuleSet.test_rule``. Changelog ========= ``v1.2.1`` - 2017/05/13 - Reverted "Fixed undesired caching in `is_group_member` factory" ``v1.2.0`` - 2016/12/18 - Added logging to predicates - Added support for Django 1.10 - Fixed undesired caching in `is_group_member` factory ``v1.1.1`` - 2015/12/07 - Improved handling of skipped predicates ``v1.1.0`` - 2015/12/05 - Fixed regression that wouldn't short-circuit boolean expressions - Added support for Django 1.9 and Python 3.5 - Added support for skipping predicates simply by returning ``None``. The previous way of skipping predicates by raising ``SkipPredicate`` has been deprecated and will not be supported in a future release. ``v1.0.0`` - 2015/10/06 - Initial stable public release - Dropped support for Python 3.2 - Added Django test suite - Added function-based view decorator - Added class-based view mixin ``v0.4`` - 2015/02/16 - Added support for creating predicates from partial functions - Added support for creating predicates from instance methods - Added predicate invocation context - Added support for automatically passing ``self`` to a predicate - Added support for discarding a predicate's result ``v0.3`` - 2014/10/15 - Added compatibility with PyPy and PyPy 3 - Added ``always_true()`` and ``always_false()`` predicates - Added integration with Tox - Bug fixes ``v0.2`` - 2014/06/09 - Added compatibility with Python 3.4 - Improved admin integration ``v0.1`` - 2014/03/07 - Initial public release Licence ======= ``django-rules`` is distributed under the MIT licence. Copyright (c) 2014 Akis Kesoglou Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.