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Mon Jan 26 15:20:26 2009 UTC (4 years, 3 months ago) by
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A few extra tests in combination with computed defaults.
Directives
==========
When grokking a class, the grokking procedure can be informed by
directives, on a class, or a module. If a directive is absent, the
system falls back to a default. Here we introduce a general way to
define these directives, and how to use them to retrieve information
for a class for use during the grokking procedure.
A simple directive
------------------
We define a simple directive that sets a description::
>>> from martian import Directive, CLASS, ONCE
>>> class description(Directive):
... scope = CLASS
... store = ONCE
... default = u''
The name of the directive is ``description``. We specify that the
directive can only be used in the scope of a class. We also specify it
can only be used a single time. Finally we define the default in case
the directive is absent (the empty string).
Now we look at the directive in action::
>>> class Foo(object):
... description(u"This is a description")
After setting the description, we bind the directive and obtain a
bound directive object. This object has means for retrieving the data
set by the directive, in particular the ``get`` method::
>>> description.bind().get(Foo)
u'This is a description'
Directives in different namespaces get stored differently. We'll
define a similar directive in another namespace::
>>> class description2(description):
... pass
>>> class Foo(object):
... description(u"Description1")
... description2(u"Description2")
>>> description.bind().get(Foo)
u'Description1'
>>> description2.bind().get(Foo)
u'Description2'
If we check the value of a class without the directive, we see the
default value for that directive, this case the empty unicode string::
>>> class Foo(object):
... pass
>>> description.bind().get(Foo)
u''
In certain cases we need to set a value on a component as if the directive was
actually used::
>>> description.set(Foo, u'value as set')
>>> description.bind().get(Foo)
u'value as set'
Subclasses of the original class will inherit the properties set by the
directive:
>>> class Foo(object):
... description('This is a foo.')
...
>>> class Bar(Foo):
... pass
...
>>> description.bind().get(Bar)
'This is a foo.'
When we use the directive outside of class scope, we get an error
message::
>>> description('Description')
Traceback (most recent call last):
...
GrokImportError: The 'description' directive can only be used on class level.
In particular, we cannot use it in a module::
>>> class testmodule(FakeModule):
... fake_module = True
... description("Description")
Traceback (most recent call last):
...
GrokImportError: The 'description' directive can only be used on class level.
We cannot use the directive twice in the class scope. If we do so, we
get an error message as well::
>>> class Foo(object):
... description(u"Description1")
... description(u"Description2")
Traceback (most recent call last):
...
GrokImportError: The 'description' directive can only be called once per class.
We cannot call the directive with no argument either::
>>> class Foo(object):
... description()
Traceback (most recent call last):
...
TypeError: description takes exactly 1 argument (0 given)
Class and module scope
----------------------
We define a ``layer`` directive that can be used in class and module
scope both::
>>> from martian import CLASS_OR_MODULE
>>> class layer(Directive):
... scope = CLASS_OR_MODULE
... store = ONCE
By default, the ``default`` property is None which is why we can omit
specifying it here.
This directive has been declared ``CLASS_OR_MODULE``, so you will
always have to pass a module to the directive. Since we don't have a
module yet we'll simply create a dummy, empty, fallback module::
>>> dummy = object()
We can use this directive now on a class::
>>> class Foo(object):
... layer('Test')
>>> layer.bind().get(Foo, dummy)
'Test'
The defaulting to ``None`` works::
>>> class Foo(object):
... pass
>>> layer.bind().get(Foo, dummy) is None
True
We can also use it in a module::
>>> class testmodule(FakeModule):
... layer('Test2')
... class Foo(object):
... pass
>>> from martiantest.fake import testmodule
When we now try to access ``layer`` on ``Foo``, we find the
module-level default which we just set. We pass the module as the
second argument to the ``get`` method to have it fall back on this::
>>> layer.bind().get(testmodule.Foo, testmodule)
'Test2'
Let's look at a module where the directive is not used::
>>> class testmodule(FakeModule):
... class Foo(object):
... pass
>>> from martiantest.fake import testmodule
In this case, the value cannot be found so the system falls back on
the default, ``None``::
>>> layer.bind().get(testmodule.Foo, testmodule) is None
True
Let's now look at this using a directive with CLASS scope only::
>>> class layer2(Directive):
... scope = CLASS
... store = ONCE
Inheritance in combination with module scope
--------------------------------------------
Let's look at how our layer directive can inherit in combination with
directive use on module scope.
First we define a module which defines a class that gets the ``Test``
layer through the use of the layer directive on module scope::
>>> class inheritmodule1(FakeModule):
... layer('Test')
... class Foo(object):
... pass
>>> from martiantest.fake import inheritmodule1
Now we define another module that has a class that inherits from ``Foo``::
>>> class inheritmodule2(FakeModule):
... class Bar(inheritmodule1.Foo):
... pass
>>> from martiantest.fake import inheritmodule2
We will now see that ``Bar`` has inherited the layer ``Test``::
>>> layer.bind().get(inheritmodule2.Bar, inheritmodule2)
'Test'
Let's try it with another level of inheritance::
>>> class inheritmodule3(FakeModule):
... class Baz(inheritmodule2.Bar):
... pass
>>> from martiantest.fake import inheritmodule3
The layer should still be inherited::
>>> layer.bind().get(inheritmodule3.Baz, inheritmodule3)
'Test'
Let's override now by having an explicit layer directive on the class
that subclasses ``Foo``::
>>> class inheritmodule4(FakeModule):
... class OverrideFoo(inheritmodule1.Foo):
... layer('AnotherTest')
>>> from martiantest.fake import inheritmodule4
>>> layer.bind().get(inheritmodule4.OverrideFoo, inheritmodule4)
'AnotherTest'
Let's override now by having an explicit layer directive on
module-level instead::
>>> class inheritmodule5(FakeModule):
... layer('AnotherTest')
... class OverrideFoo(inheritmodule1.Foo):
... pass
>>> from martiantest.fake import inheritmodule5
>>> layer.bind().get(inheritmodule5.OverrideFoo, inheritmodule5)
'AnotherTest'
Using a directive multiple times
--------------------------------
A directive can be configured to allow it to be called multiple times
in the same scope::
>>> from martian import MultipleTimesDirective
>>> class multi(MultipleTimesDirective):
... scope = CLASS
We can now use the directive multiple times without any errors::
>>> class Foo(object):
... multi(u"Once")
... multi(u"Twice")
We can now retrieve the value and we'll get a list::
>>> multi.bind().get(Foo)
[u'Once', u'Twice']
The default value for a MultipleTimesDirective is an empty list::
>>> class Bar(object):
... pass
>>> multi.bind().get(Bar)
[]
Whenever the directive is used on a sub class of a component, the values set by
directives on the base classes are combined::
>>> class Qux(Foo):
... multi(u'Triple')
...
>>> multi.bind().get(Qux)
[u'Once', u'Twice', u'Triple']
You can also create a directive that ignores the values on the base classes::
>>> from martian import MULTIPLE_NOBASE
>>> class multi(Directive):
... scope = CLASS
... store = MULTIPLE_NOBASE
>>> class Foo(object):
... multi(u"Once")
... multi(u"Twice")
>>> multi.bind().get(Foo)
[u'Once', u'Twice']
>>> class Qux(Foo):
... multi(u'Triple')
... multi(u'More')
>>> multi.bind().get(Qux)
[u'Triple', u'More']
Using a directive multiple times, as a dictionary
-------------------------------------------------
A directive can be configured to allow it to be called multiple times in the
same scope. In this case the factory method should be overridden to return a
key-value pair::
>>> from martian import DICT
>>> class multi(Directive):
... scope = CLASS
... store = DICT
... def factory(self, value):
... return value.lower(), value
We can now use the directive multiple times without any errors::
>>> class Bar(object):
... multi(u"Once")
... multi(u"Twice")
We can now retrieve the value and we'll get a to the items::
>>> d = multi.bind().get(Bar)
>>> print sorted(d.items())
[(u'once', u'Once'), (u'twice', u'Twice')]
When the factory method does not return a key-value pair, an error is raised::
>>> class wrongmulti(Directive):
... scope = CLASS
... store = DICT
... def factory(self, value):
... return None
>>> class Baz(object):
... wrongmulti(u"Once")
Traceback (most recent call last):
...
GrokImportError: The factory method for the 'wrongmulti' directive should
return a key-value pair.
>>> class wrongmulti2(Directive):
... scope = CLASS
... store = DICT
... def factory(self, value):
... return value, value, value
>>> class Baz(object):
... wrongmulti2(u"Once")
Traceback (most recent call last):
...
GrokImportError: The factory method for the 'wrongmulti2' directive should
return a key-value pair.
Like with MULTIPLE store, values set by directives using the DICT store are
combined::
>>> class multi(Directive):
... scope = CLASS
... store = DICT
... def factory(self, value, andanother):
... return value, andanother
...
>>> class Frepple(object):
... multi(1, 'AAA')
... multi(2, 'BBB')
...
>>> class Fropple(Frepple):
... multi(1, 'CCC')
... multi(3, 'DDD')
... multi(4, 'EEE')
>>> d = multi.bind().get(Fropple)
>>> print sorted(d.items())
[(1, 'CCC'), (2, 'BBB'), (3, 'DDD'), (4, 'EEE')]
Using MULTIPLE and DICT can also work on a module level, even though
inheritance has no meaning there::
>>> from martian import MODULE
>>> class multi(MultipleTimesDirective):
... scope = MODULE
...
>>> multi.__module__ = 'somethingelse'
>>> class module_with_directive(FakeModule):
... fake_module = True
...
... multi('One')
... multi('Two')
...
>>> from martiantest.fake import module_with_directive
>>> print multi.bind().get(module=module_with_directive)
['One', 'Two']
>>> from martian import MODULE
>>> class multi(Directive):
... scope = MODULE
... store = DICT
... def factory(self, value, andanother):
... return value, andanother
...
>>> multi.__module__ = 'somethingelse'
>>> class module_with_directive(FakeModule):
... fake_module = True
...
... multi(1, 'One')
... multi(2, 'Two')
...
>>> from martiantest.fake import module_with_directive
>>> d = multi.bind().get(module=module_with_directive)
>>> print sorted(d.items())
[(1, 'One'), (2, 'Two')]
Calculated defaults
-------------------
Often instead of just supplying the system with a default, we want to
calculate the default in some way. We define the ``name`` directive,
which if not present, will calculate its value from the name of class,
lower-cased. Instead of passing a default value, we pass a function as the
default argument::
>>> class name(Directive):
... scope = CLASS
... store = ONCE
...
>>> def default_name_lowercase(component, module, **data):
... return component.__name__.lower()
...
>>> bound_name = name.bind(get_default=default_name_lowercase)
>>> class Foo(object):
... name('bar')
>>> bound_name.get(Foo)
'bar'
>>> class Foo(object):
... pass
>>> bound_name.get(Foo)
'foo'
Calculated defaults in combination with inheritance
---------------------------------------------------
Calculated defaults should not kick in when we can actually find a
value due to inheritance of a module-level directive. Let's set up a
situation that has this inheritance::
>>> class inheritmodule1(FakeModule):
... layer('Test')
... class Foo(object):
... pass
>>> from martiantest.fake import inheritmodule1
>>> class inheritmodule2(FakeModule):
... class Bar(inheritmodule1.Foo):
... pass
>>> from martiantest.fake import inheritmodule2
We define a way to compute the default::
>>> def our_get_default(component, module, **data):
... return "the computed default"
We don't expect the default rule to kick in as we can find an explicitly
set value::
>>> layer.bind(get_default=our_get_default).get(inheritmodule2.Bar, inheritmodule2)
'Test'
Let's now consider a case where we have inheritance without explicit use
of the directive::
>>> class inheritmodule1(FakeModule):
... class Foo(object):
... pass
>>> from martiantest.fake import inheritmodule1
>>> class inheritmodule2(FakeModule):
... class Bar(inheritmodule1.Foo):
... pass
>>> from martiantest.fake import inheritmodule2
>>> layer.bind(get_default=our_get_default).get(inheritmodule2.Bar, inheritmodule2)
'the computed default'
A marker directive
------------------
Another type of directive is a marker directive. This directive takes
no arguments at all, but when used it marks the context::
>>> from martian import MarkerDirective
>>> class mark(MarkerDirective):
... scope = CLASS
>>> class Foo(object):
... mark()
Class ``Foo`` is now marked::
>>> mark.bind().get(Foo)
True
When we have a class that isn't marked, we get the default value, ``False``::
>>> class Bar(object):
... pass
>>> mark.bind().get(Bar)
False
If we pass in an argument, we get an error::
>>> class Bar(object):
... mark("An argument")
Traceback (most recent call last):
...
TypeError: mark takes no arguments (1 given)
Validation
----------
A directive can be supplied with a validation method. The validation method
checks whether the value passed in is allowed. It should raise
``GrokImportError`` if the value cannot be validated, together with a
description of why not.
First we define our own validation function. A validation function
takes two arguments:
* the name of the directive we're validating for
* the value we need to validate
The name can be used to format the exception properly.
We'll define a validation method that only expects integer numbers::
>>> from martian.error import GrokImportError
>>> class number(Directive):
... scope = CLASS
... store = ONCE
... def validate(self, value):
... if type(value) is not int:
... raise GrokImportError("The '%s' directive can only be called with an integer." %
... self.name)
>>> class Foo(object):
... number(3)
>>> class Foo(object):
... number("This shouldn't work")
Traceback (most recent call last):
...
GrokImportError: The 'number' directive can only be called with an integer.
Some built-in validation functions
----------------------------------
Let's look at some built-in validation functions.
The ``validateText`` function determines whether a string
is unicode or plain ascii::
>>> from martian import validateText
>>> class title(Directive):
... scope = CLASS
... store = ONCE
... default = u''
... validate = validateText
When we pass ascii text into the directive, there is no error::
>>> class Foo(object):
... title('Some ascii text')
We can also pass in a unicode string without error::
>>> class Foo(object):
... title(u'Some unicode text')
Let's now try it with something that's not text at all, such as a number.
This fails::
>>> class Foo(object):
... title(123)
Traceback (most recent call last):
...
GrokImportError: The 'title' directive can only be called with unicode or ASCII.
It's not allowed to call the direct with a non-ascii encoded string::
>>> class Foo(object):
... title(u'è'.encode('latin-1'))
Traceback (most recent call last):
...
GrokImportError: The 'title' directive can only be called with unicode or ASCII.
>>> class Foo(object):
... title(u'è'.encode('UTF-8'))
Traceback (most recent call last):
...
GrokImportError: The 'title' directive can only be called with unicode or ASCII.
The ``validateInterfaceOrClass`` function only accepts class or
interface objects::
>>> from martian import validateInterfaceOrClass
>>> class klass(Directive):
... scope = CLASS
... store = ONCE
... validate = validateInterfaceOrClass
It works with interfaces and classes::
>>> class Bar(object):
... pass
>>> class Foo(object):
... klass(Bar)
>>> from zope.interface import Interface
>>> class IBar(Interface):
... pass
>>> class Foo(object):
... klass(IBar)
It won't work with other things::
>>> class Foo(object):
... klass(Bar())
Traceback (most recent call last):
...
GrokImportError: The 'klass' directive can only be called with a class or an interface.
>>> class Foo(object):
... klass(1)
Traceback (most recent call last):
...
GrokImportError: The 'klass' directive can only be called with a class or an interface.
The ``validateInterface`` validator only accepts an interface::
>>> from martian import validateInterface
>>> class iface(Directive):
... scope = CLASS
... store = ONCE
... validate = validateInterface
Let's try it::
>>> class Foo(object):
... iface(IBar)
It won't work with classes or other things::
>>> class Foo(object):
... iface(Bar)
Traceback (most recent call last):
...
GrokImportError: The 'iface' directive can only be called with an interface.
>>> class Foo(object):
... iface(1)
Traceback (most recent call last):
...
GrokImportError: The 'iface' directive can only be called with an interface.
The ``validateClass`` validator only accepts a class::
>>> from martian import validateClass
>>> class klass(Directive):
... scope = CLASS
... store = ONCE
... validate = validateClass
>>> class Foo(object):
... klass(Bar)
But it won't work with an interface or other things::
>>> class Foo(object):
... klass(IBar)
Traceback (most recent call last):
...
GrokImportError: The 'klass' directive can only be called with a class.
>>> class Foo(object):
... klass(Bar())
Traceback (most recent call last):
...
GrokImportError: The 'klass' directive can only be called with a class.
Declaring base classes
----------------------
There's a special directive called ``martian.baseclass`` which lets
you declare that a certain class is the base class for a series of
other components. This property should not be inherited by those
components. Consider the following base class:
>>> import martian
>>> class MyBase(object):
... martian.baseclass()
As you would expect, the directive will correctly identify this class as a
baseclass:
>>> martian.baseclass.bind().get(MyBase)
True
But, if we create a subclass of this base class, the subclass won't inherit
that property, unlike with a regular directive:
>>> class SubClass(MyBase):
... pass
...
>>> martian.baseclass.bind().get(SubClass)
False
Naturally, the directive will also report a false answer if the class doesn't
inherit from a base class at all and hasn't been marked with the directive:
>>> class NoBase(object):
... pass
...
>>> martian.baseclass.bind().get(NoBase)
False
