python-martian 0.14-0ubuntu1 / usr / share / pyshared / martian-0.14.egg-info / PKG-INFO

Metadata-Version: 1.0
Name: martian
Version: 0.14
Summary: Martian is a library that allows the embedding of configuration
information in Python code. Martian can then grok the system and
do the appropriate configuration registrations. One example of a system
that uses Martian is the system where it originated: Grok
(http://grok.zope.org)

Home-page: UNKNOWN
Author: Grok project
Author-email: grok-dev@zope.org
License: ZPL
Description: *******
        Martian
        *******
        
        A library to grok configuration from Python code.
        
        Martian tutorial
        ****************
        
        Introduction
        ============
        
        "There was so much to grok, so little to grok from." -- Stranger in a
        Strange Land, by Robert A. Heinlein
        
        Martian provides infrastructure for declarative configuration of
        Python code. Martian is especially useful for the construction of
        frameworks that need to provide a flexible plugin
        infrastructure. Martian doesn't actually provide infrastructure for
        plugin registries (except for itself). Many frameworks have their own
        systems for this, and if you need a generic one, you might want to
        consider ``zope.component``. Martian just allows you to make the
        registration of plugins less verbose.
        
        You can see Martian as doing something that you can also solve with
        metaclasses, with the following advantages:
        
        * the developer of the framework doesn't have to write a lot of ad-hoc
          metaclasses anymore; instead we offer an infrastructure to make life
          easier.
        
        * configuration doesn't need to happen at import time, but can happen at
          program startup time. This also makes configuration more tractable for
          a developer.
        
        * we don't bother the developer that *uses* the framework with the
          surprising behavior that metaclasses sometimes bring. The classes
          the user has to deal with are normal classes.
        
        Why is this package named ``martian``? In the novel "Stranger in a
        Strange Land", the verb *grok* is introduced:
        
          Grok means to understand so thoroughly that the observer becomes a
          part of the observed -- to merge, blend, intermarry, lose identity
          in group experience.
        
        In the context of this package, "grokking" stands for the process of
        deducing declarative configuration actions from Python code. In the
        novel, grokking is originally a concept that comes from the planet
        Mars. Martians *grok*. Since this package helps you grok code, it's
        called Martian.
        
        Martian provides a framework that allows configuration to be expressed
        in declarative Python code. These declarations can often be deduced
        from the structure of the code itself. The idea is to make these
        declarations so minimal and easy to read that even extensive
        configuration does not overly burden the programmers working with the
        code.
        
        The ``martian`` package is a spin-off from the `Grok project`_, in the
        context of which this codebase was first developed. While Grok uses
        it, the code is completely independent of Grok.
        
        .. _`Grok project`: http://grok.zope.org
        
        Motivation
        ==========
        
        "Deducing declarative configuration actions from Python code" - that
        sounds very abstract. What does it actually mean? What is
        configuration?  What is declarative configuration? In order to explain
        this, we'll first take a look at configuration.
        
        Larger frameworks often offer a lot of points where you can modify
        their behavior: ways to combine its own components with components you
        provide yourself to build a larger application. A framework offers
        points where it can be *configured* with plugin code. When you plug
        some code into a plugin point, it results in the updating of some
        registry somewhere with the new plugin. When the framework uses a
        plugin, it will first look it up in the registry. The action of
        registering some component into a registry can be called
        *configuration*.
        
        Let's look at an example framework that offers a plugin point. We
        introduce a very simple framework for plugging in different template
        languages, where each template language uses its own extension. You
        can then supply the framework with the template body and the template
        extension and some data, and render the template.
        
        Let's look at the framework::
        
          >>> import string
          >>> class templating(FakeModule):
          ...
          ...   class InterpolationTemplate(object):
          ...      "Use %(foo)s for dictionary interpolation."
          ...      def __init__(self, text):
          ...          self.text = text
          ...      def render(self, **kw):
          ...          return self.text % kw
          ...
          ...   class TemplateStringTemplate(object):
          ...      "PEP 292 string substitutions."
          ...      def __init__(self, text):
          ...          self.template = string.Template(text)
          ...      def render(self, **kw):
          ...          return self.template.substitute(**kw)
          ...
          ...   # the registry, we plug in the two templating systems right away
          ...   extension_handlers = { '.txt': InterpolationTemplate, 
          ...                          '.tmpl': TemplateStringTemplate }
          ...
          ...   def render(data, extension, **kw):
          ...      """Render the template at filepath with arguments.
          ...  
          ...      data - the data in the file
          ...      extension - the extension of the file
          ...      keyword arguments - variables to interpolate
          ...
          ...      In a real framework you could pass in the file path instead of
          ...      data and extension, but we don't want to open files in our
          ...      example.
          ...
          ...      Returns the rendered template
          ...      """
          ...      template = extension_handlers[extension](data)
          ...      return template.render(**kw)
        
        Since normally we cannot create modules in a doctest, we have emulated
        the ``templating`` Python module using the ``FakeModule``
        class. Whenever you see ``FakeModule`` subclasses, imagine you're
        looking at a module definition in a ``.py`` file. Now that we have
        defined a module ``templating``, we also need to be able to import
        it. Fake modules are always placed automatically into the
        ``martiantest.fake`` namespace so you can import them from there::
        
          >>> from martiantest.fake import templating
        
        Now let's try the ``render`` function for the registered template
        types, to demonstrate that our framework works::
        
          >>> templating.render('Hello %(name)s!', '.txt', name="world")
          'Hello world!'
          >>> templating.render('Hello ${name}!', '.tmpl', name="universe")
          'Hello universe!'
        
        File extensions that we do not recognize cause a ``KeyError`` to be
        raised::
        
          >>> templating.render('Hello', '.silly', name="test")
          Traceback (most recent call last):
          ...
          KeyError: '.silly'
        
        We now want to plug into this filehandler framework and provide a
        handler for ``.silly`` files. Since we are writing a plugin, we cannot
        change the ``templating`` module directly. Let's write an extension
        module instead::
        
          >>> class sillytemplating(FakeModule):
          ...   class SillyTemplate(object):
          ...      "Replace {key} with dictionary values."
          ...      def __init__(self, text):
          ...          self.text = text
          ...      def render(self, **kw):
          ...          text = self.text
          ...          for key, value in kw.items():
          ...              text = text.replace('{%s}' % key, value)
          ...          return text
          ...
          ...   templating.extension_handlers['.silly'] = SillyTemplate
          >>> from martiantest.fake import sillytemplating
        
        In the extension module, we manipulate the ``extension_handlers``
        dictionary of the ``templating`` module (in normal code we'd need to
        import it first), and plug in our own function. ``.silly`` handling
        works now::
        
          >>> templating.render('Hello {name}!', '.silly', name="galaxy")
          'Hello galaxy!'
        
        Above we plug into our ``extension_handler`` registry using Python
        code. Using separate code to manually hook components into registries
        can get rather cumbersome - each time you write a plugin, you also
        need to remember you need to register it. 
        
        Doing template registration in Python code also poses a maintenance
        risk. It is tempting to start doing fancy things in Python code such
        as conditional configuration, making the configuration state of a
        program hard to understand. Another problem is that doing
        configuration at import time can also lead to unwanted side effects
        during import, as well as ordering problems, where you want to import
        something that really needs configuration state in another module that
        is imported later. Finally, it can also make code harder to test, as
        configuration is loaded always when you import the module, even if in
        your test perhaps you don't want it to be.
        
        Martian provides a framework that allows configuration to be expressed
        in declarative Python code. Martian is based on the realization that
        what to configure where can often be deduced from the structure of
        Python code itself, especially when it can be annotated with
        additional declarations. The idea is to make it so easy to write and
        register a plugin so that even extensive configuration does not overly
        burden the developer. 
        
        Configuration actions are executed during a separate phase ("grok
        time"), not at import time, which makes it easier to reason about and
        easier to test.
        
        Configuration the Martian Way
        =============================
        
        Let's now transform the above ``templating`` module and the
        ``sillytemplating`` module to use Martian. First we must recognize
        that every template language is configured to work for a particular
        extension. With Martian, we annotate the classes themselves with this
        configuration information. Annotations happen using *directives*,
        which look like function calls in the class body.
        
        Let's create an ``extension`` directive that can take a single string
        as an argument, the file extension to register the template class
        for::
        
          >>> import martian
          >>> class extension(martian.Directive):
          ...   scope = martian.CLASS
          ...   store = martian.ONCE
          ...   default = None
        
        We also need a way to easily recognize all template classes. The normal
        pattern for this in Martian is to use a base class, so let's define a
        ``Template`` base class::
        
          >>> class Template(object):
          ...   pass
        
        We now have enough infrastructure to allow us to change the code to use
        Martian style base class and annotations::
        
          >>> class templating(FakeModule):
          ...
          ...   class InterpolationTemplate(Template):
          ...      "Use %(foo)s for dictionary interpolation."
          ...      extension('.txt')
          ...      def __init__(self, text):
          ...          self.text = text
          ...      def render(self, **kw):
          ...          return self.text % kw
          ...
          ...   class TemplateStringTemplate(Template):
          ...      "PEP 292 string substitutions."
          ...      extension('.tmpl')
          ...      def __init__(self, text):
          ...          self.template = string.Template(text)
          ...      def render(self, **kw):
          ...          return self.template.substitute(**kw)
          ...
          ...   # the registry, empty to start with
          ...   extension_handlers = {}
          ...
          ...   def render(data, extension, **kw):
          ...      # this hasn't changed
          ...      template = extension_handlers[extension](data)
          ...      return template.render(**kw)
          >>> from martiantest.fake import templating
        
        As you can see, there have been very few changes:
        
        * we made the template classes inherit from ``Template``.
        
        * we use the ``extension`` directive in the template classes.
        
        * we stopped pre-filling the ``extension_handlers`` dictionary.
        
        So how do we fill the ``extension_handlers`` dictionary with the right
        template languages? Now we can use Martian. We define a *grokker* for
        ``Template`` that registers the template classes in the
        ``extension_handlers`` registry::
        
          >>> class meta(FakeModule):   
          ...   class TemplateGrokker(martian.ClassGrokker):
          ...     martian.component(Template)
          ...     martian.directive(extension)
          ...     def execute(self, class_, extension, **kw):
          ...       templating.extension_handlers[extension] = class_
          ...       return True
          >>> from martiantest.fake import meta
        
        What does this do? A ``ClassGrokker`` has its ``execute`` method
        called for subclasses of what's indicated by the ``martian.component``
        directive. You can also declare what directives a ``ClassGrokker``
        expects on this component by using ``martian.directive()`` (the
        ``directive`` directive!) one or more times. 
        
        The ``execute`` method takes the class to be grokked as the first
        argument, and the values of the directives used will be passed in as
        additional parameters into the ``execute`` method. The framework can
        also pass along an arbitrary number of extra keyword arguments during
        the grokking process, so we need to declare ``**kw`` to make sure we
        can handle these.
        
        All our grokkers will be collected in a special Martian-specific
        registry::
        
          >>> reg = martian.GrokkerRegistry()
        
        We will need to make sure the system is aware of the
        ``TemplateGrokker`` defined in the ``meta`` module first, so let's
        register it first. We can do this by simply grokking the ``meta``
        module::
        
          >>> reg.grok('meta', meta)
          True
        
        Because ``TemplateGrokker`` is now registered, our registry now knows
        how to grok ``Template`` subclasses. Let's grok the ``templating``
        module::
        
          >>> reg.grok('templating', templating)
          True
        
        Let's try the ``render`` function of templating again, to demonstrate
        we have successfully grokked the template classes::
        
          >>> templating.render('Hello %(name)s!', '.txt', name="world")
          'Hello world!'
          >>> templating.render('Hello ${name}!', '.tmpl', name="universe")
          'Hello universe!'
        
        ``.silly`` hasn't been registered yet::
        
          >>> templating.render('Hello', '.silly', name="test")
          Traceback (most recent call last):
          ...
          KeyError: '.silly'
        
        Let's now register ``.silly`` from an extension module::
        
          >>> class sillytemplating(FakeModule):
          ...   class SillyTemplate(Template):
          ...      "Replace {key} with dictionary values."
          ...      extension('.silly')
          ...      def __init__(self, text):
          ...          self.text = text
          ...      def render(self, **kw):
          ...          text = self.text
          ...          for key, value in kw.items():
          ...              text = text.replace('{%s}' % key, value)
          ...          return text
          >>> from martiantest.fake import sillytemplating
        
        As you can see, the developer that uses the framework has no need
        anymore to know about ``templating.extension_handlers``. Instead we can
        simply grok the module to have ``SillyTemplate`` be register appropriately::
        
          >>> reg.grok('sillytemplating', sillytemplating)
          True
        
        We can now use the ``.silly`` templating engine too::
        
          >>> templating.render('Hello {name}!', '.silly', name="galaxy")
          'Hello galaxy!'
        
        Admittedly it is hard to demonstrate Martian well with a small example
        like this. In the end we have actually written more code than in the
        basic framework, after all. But even in this small example, the
        ``templating`` and ``sillytemplating`` module have become more
        declarative in nature. The developer that uses the framework will not
        need to know anymore about things like
        ``templating.extension_handlers`` or an API to register things
        there. Instead the developer can registering a new template system
        anywhere, as long as he subclasses from ``Template``, and as long as
        his code is grokked by the system.
        
        Finally note how Martian was used to define the ``TemplateGrokker`` as
        well. In this way Martian can use itself to extend itself.
        
        Grokking instances
        ==================
        
        Above we've seen how you can grok classes. Martian also supplies a way
        to grok instances. This is less common in typical frameworks, and has
        the drawback that no class-level directives can be used, but can still
        be useful.
        
        Let's imagine a case where we have a zoo framework with an ``Animal``
        class, and we want to track instances of it::
        
          >>> class Animal(object):
          ...   def __init__(self, name):
          ...     self.name = name
          >>> class zoo(FakeModule):
          ...   horse = Animal('horse')
          ...   chicken = Animal('chicken')
          ...   elephant = Animal('elephant')
          ...   lion = Animal('lion')
          ...   animals = {}
          >>> from martiantest.fake import zoo
         
        We define an ``InstanceGrokker`` subclass to grok ``Animal`` instances::
        
          >>> class meta(FakeModule):   
          ...   class AnimalGrokker(martian.InstanceGrokker):
          ...     martian.component(Animal)
          ...     def execute(self, instance, **kw):
          ...       zoo.animals[instance.name] = instance
          ...       return True
          >>> from martiantest.fake import meta
        
        Let's create a new registry with the ``AnimalGrokker`` in it::
           
          >>> reg = martian.GrokkerRegistry()
          >>> reg.grok('meta', meta)
          True
        
        We can now grok the ``zoo`` module::
        
          >>> reg.grok('zoo', zoo)
          True
        
        The animals will now be in the ``animals`` dictionary::
        
          >>> sorted(zoo.animals.items())
          [('chicken', <Animal object at ...>), 
           ('elephant', <Animal object at ...>), 
           ('horse', <Animal object at ...>), 
           ('lion', <Animal object at ...>)]
        
        More information
        ================
        
        For many more details and examples of more kinds of grokkers, please
        see ``src/martian/core.txt``. For more information on directives see
        ``src/martian/directive.txt``.
        
        CHANGES
        *******
        
        0.14 (2010-11-03)
        =================
        
        Feature changes
        ---------------
        
        * The computation of the default value for a directive can now be defined inside
          the directive class definition. Whenever there is a ``get_default``
          classmethod, it is used for computing the default::
        
              class name(Directive):
                  scope = CLASS
                  store = ONCE
        
                  @classmethod
                  def get_default(cls, component, module=None, **data):
                     return component.__name__.lower()
        
          When binding the directive, the default-default behaviour can still be
          overriden by passing a ``get_default`` function::
        
              def another_default(component, module=None, **data):
                 return component.__name__.lower()
        
              name.bind(get_default=another_default).get(some_component)
        
          Making the default behaviour intrinsic to the directive, prevents having to
          pass the ``get_default`` function over and over when getting values, for
          example in the grokkers.
        
        0.13 (2010-11-01)
        =================
        
        Feature changes
        ---------------
        
        * Ignore all __main__ modules.
        
        * List zope.testing as a test dependency.
        
        0.12 (2009-06-29)
        =================
        
        Feature changes
        ---------------
        
        * Changes to better support various inheritance scenarios in combination with
          directives. Details follow.
        
        * ``CLASS_OR_MODULE`` scope directives will be aware of inheritance of
          values that are defined in module-scope. Consider the following case::
        
            module a:
              some_directive('A')
              class Foo(object):
                pass
        
            module b:
              import a
              class Bar(a.Foo):
                pass
        
          As before, ``Foo`` will have the value ``A`` configured for it. ``Bar``,
          since it inherits from ``Foo``, will inherit this value.
        
        * ``CLASS_OR_MODULE`` and ``CLASS`` scope directives will be aware of
          inheritance of computed default values. Consider the following case::
        
            module a:
              class Foo(object):
                 pass
        
            module b:
              import a
              class Bar(a.Foo):
                 pass
        
            def get_default(component, module, **data):
                if module.__name__ == 'a':
                   return "we have a default value for module a"
                return martian.UNKNOWN
        
          When we now do this::
        
            some_directive.bind(get_default=get_default).get(b.Bar)
        
          We will get the value "we have a default value for module a". This
          is because when trying to compute the default value for ``Bar`` we
          returned ``martian.UNKNOWN`` to indicate the value couldn't be found
          yet. The system then looks at the base class and tries again, and in
          this case it succeeds (as the module-name is ``a``).
        
        * ``martian.ONCE_IFACE`` storage option to allow the creation of
          directives that store their value on ``zope.interface``
          interfaces. This was originally in ``grokcore.view`` but was of
          wider usefulness.
        
        Bugs fixed
        ----------
        
        * Ignore things that look like Python modules and packages but aren't.
          These are sometimes created by editors, operating systems and
          network file systems and we don't want to confuse them.
        
        * Ignore .pyc and .pyo files that don't have a matching .py file via
          ``module_info_from_dotted_name`` if its ``ignore_nonsource``
          parameter is ``True``.  The default is ``True``.  To revert to the
          older behavior where .pyc files were honored, pass
          ``ignore_nonsource=False``.
        
        * Pass along ``exclude_filter`` (and the new ``ignore_nonsource``
          flag) to ModuleInfo constructor when it calls itself recursively.
        
        * Replace ``fake_import`` to import fake modules in tests with a real
          python import statement (``from martiantest.fake import
          my_fake_module``). This works by introducing a metaclass for
          ``FakeModule`` that automatically registers it as a module. The
          irony does not escape us. This also means that
          ``martian.scan.resolve()`` will now work on fake modules.
        
        0.11 (2008-09-24)
        =================
        
        Feature changes
        ---------------
        
        * Added MULTIPLE_NOBASE option for directive store. This is like MULTIPLE
          but doesn't inherit information from the base class.
        
        0.10 (2008-06-06)
        =================
        
        Feature changes
        ---------------
        
        * Add a ``validateClass`` validate function for directives.
        
        * Moved ``FakeModule`` and ``fake_import`` into a ``martian.testing``
          module so that they can be reused by external packages.
        
        * Introduce new tutorial text as README.txt. The text previously in
          ``README.txt`` was rather too detailed for a tutorial, so has been
          moved into ``core.txt``.
        
        * Introduce a ``GrokkerRegistry`` class that is a ``ModuleGrokker``
          with a ``MetaMultiGrokker`` in it. This is the convenient thing to
          instantiate to start working with Grok and is demonstrated in the
          tutorial.
        
        * Introduced three new martian-specific directives:
          ``martian.component``, ``martian.directive`` and
          ``martian.priority``. These replace the ``component_class``,
          ``directives`` and ``priority`` class-level attributes. This way
          Grokkers look the same as what they grok. This breaks backwards
          compatibility again, but it's an easy replace operation. Note that
          ``martian.directive`` takes the directive itself as an argument, and
          then optionally the same arguments as the ``bind`` method of
          directives (``name``, ``default`` and ``get_default``). It may be
          used multiple times. Note that ``martian.baseclass`` was already a
          Martian-specific directive and this has been unchanged.
        
        * For symmetry, add an ``execute`` method to ``InstanceGrokker``.
        
        0.9.7 (2008-05-29)
        ==================
        
        Feature changes
        ---------------
        
        * Added a ``MethodGrokker`` base class for grokkers that want to grok
          methods of a class rather than the whole class itself.  It works
          quite similar to the ``ClassGrokker`` regarding directive
          definition, except that directives evaluated not only on class (and
          possibly module) level but also for each method.  That way,
          directives can also be applied to methods (as decorators) in case
          they support it.
        
        0.9.6 (2008-05-14)
        ==================
        
        Feature changes
        ---------------
        
        * Refactored the ``martian.Directive`` base class yet again to allow
          more declarative (rather than imperative) usage in grokkers.
          Directives themselves no longer have a ``get()`` method nor a
          default value factory (``get_default()``).  Instead you will have to
          "bind" the directive first which is typically done in a grokker.
        
        * Extended the ``ClassGrokker`` baseclass with a standard ``grok()``
          method that allows you to simply declare a set of directives that
          are used on the grokked classes.  Then you just have to implement an
          ``execute()`` method that will receive the data from those
          directives as keyword arguments.  This simplifies the implementation
          of class grokkers a lot.
        
        0.9.5 (2008-05-04)
        ==================
        
        * ``scan_for_classes`` just needs a single second argument specifying
          an interface. The support for scanning for subclasses directly has
          been removed as it became unnecessary (due to changes in
          grokcore.component).
        
        0.9.4 (2008-05-04)
        ==================
        
        Features changes
        ----------------
        
        * Replaced the various directive base classes with a single
          ``martian.Directive`` base class:
        
          - The directive scope is now defined with the ``scope`` class
            attribute using one of ``martian.CLASS``, ``martian.MODULE``,
            ``martian.CLASS_OR_MODULE``.
        
          - The type of storage is defined with the ``store`` class attribute
            using one of ``martian.ONCE``, ``martian.MULTIPLE``,
            ``martian.DICT``.
        
          - Directives have now gained the ability to read the value that they
            have set on a component or module using a ``get()`` method.  The
            ``class_annotation`` and ``class_annotation_list`` helpers have
            been removed as a consequence.
        
        * Moved the ``baseclass()`` directive from Grok to Martian.
        
        * Added a ``martian.util.check_provides_one`` helper, in analogy to
          ``check_implements_one``.
        
        * The ``scan_for_classes`` helper now also accepts an ``interface``
          argument which allows you to scan for classes based on interface
          rather than base classes.
        
        Bug fixes
        ---------
        
        * added dummy ``package_dotted_name`` to ``BuiltinModuleInfo``. This
          allows the grokking of views in test code using Grok's
          ``grok.testing.grok_component`` without a failure when it sets up the
          ``static`` attribute.
        
        * no longer use the convention that classes ending in -Base will be considered
          base classes. You must now explicitly use the grok.baseclass() directive.
        
        * The type check of classes uses isinstance() instead of type(). This means
          Grok can work with Zope 2 ExtensionClasses and metaclass programming.
        
        0.9.3 (2008-01-26)
        ==================
        
        Feature changes
        ---------------
        
        * Added an OptionalValueDirective which allows the construction of
          directives that take either zero or one argument. If no arguments
          are given, the ``default_value`` method on the directive is
          called. Subclasses need to override this to return the default value
          to use.
        
        Restructuring
        -------------
        
        * Move some util functions that were really grok-specific out of Martian
          back into Grok.
        
        0.9.2 (2007-11-20)
        ==================
        
        Bug fixes
        ---------
        
        * scan.module_info_from_dotted_name() now has special behavior when it
          runs into __builtin__. Previously, it would crash with an error. Now
          it will return an instance of BuiltinModuleInfo. This is a very
          simple implementation which provides just enough information to make
          client code work. Typically this client code is test-related so that
          the module context will be __builtin__.
        
        0.9.1 (2007-10-30)
        ==================
        
        Feature changes
        ---------------
        
        * Grokkers now receive a ``module_info`` keyword argument.  This
          change is completely backwards-compatible since grokkers which don't
          take ``module_info`` explicitly will absorb the extra argument in
          ``**kw``.
        
        0.9 (2007-10-02)
        =================
        
        Feature changes
        ---------------
        
        * Reverted the behaviour where modules called tests or ftests were skipped
          by default and added an API to provides a filtering function for skipping
          modules to be grokked.
        
        0.8.1 (2007-08-13)
        ==================
        
        Feature changes
        ---------------
        
        * Don't grok tests or ftests modules.
        
        Bugs fixed
        ----------
        
        * Fix a bug where if a class had multiple base classes, this could end up
          in the resultant list multiple times.
        
        0.8 (2007-07-02)
        ================
        
        Feature changes
        ---------------
        
        * Initial public release.
        
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