aglyph.context — Defining component contexts

Release:3.0.0.post1

The classes in this module are used to define collections (“contexts”) of related components and templates.

A context can be created in pure Python using the following API classes:

• aglyph.component.Template
• aglyph.component.Component
• aglyph.component.Reference (used to indicate that one component depends on another component)
• aglyph.component.Evaluator (used like a partial function to lazily evaluate component initialization arguments and attributes)
• aglyph.context.Context or a subclass

New in version 3.0.0: For easier programmatic configuration, refer to The Aglyph Context fluent API.

Alternatively, a context can be defined using a declarative XML syntax that conforms to the Aglyph context DTD (included in the resources/ directory of the distribution). This approach requires only the aglyph.context.XMLContext class, which parses the XML document and then uses the API classes mentioned above to populate the context.

class aglyph.context.Context(context_id, after_inject=None, before_clear=None)

Bases: dict, aglyph.context._ContextBuilder

A mapping of unique IDs to Component and Template objects.

Parameters:

• context_id (str) – an identifier for this context
• after_inject (str) – specifies the name of the method that will be called (if it exists) on all component objects after all of their dependencies have been injected
• before_clear (str) – specifies the name of the method that will be called (if it exists) on all singleton, borg, and weakref objects immediately before they are cleared from cache

register(definition)

Add a component or template definition to this context.

Parameters:definition – a Component or Template object Raises:AglyphError – if a component or template with the same unique ID is already registered in this context

Note

To replace an already-registered component or template with the same unique ID, use dict.__setitem__() directly.

get_component(component_id)

Return the Component identified by component_id.

Parameters:component_id (str) – a unique ID that identifies a Component Returns:the Component identified by component_id Return type:Component if component_id is mapped, else None

iter_components(strategy=None)

Yield all definitions in this context that are instances of Component, optionally filtered by strategy.

Parameters:strategy (str) – only yield component definitions that use this assembly strategy (by default, all component definitions are yielded) Returns:a Component generator

borg(component_id_spec, parent=None)

Return a borg Component builder for a component identified by component_id_spec.

Parameters:

• component_id_spec – a context-unique identifier for this component; or the object whose dotted name will identify this component
• parent – the context-unique identifier for this component’s parent template or component definition; or the object whose dotted name identifies this component’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

component(component_id_spec, parent=None)

Return a fluent Component builder for component_id_spec.

Parameters:

• component_id_spec – a context-unique identifier for this component; or the object whose dotted name will identify this component
• parent – the context-unique identifier for this component’s parent template or component definition; or the object whose dotted name identifies this component’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

prototype(component_id_spec, parent=None)

Return a prototype Component builder for a component identified by component_id_spec.

Parameters:

• component_id_spec – a context-unique identifier for this component; or the object whose dotted name will identify this component
• parent – the context-unique identifier for this component’s parent template or component definition; or the object whose dotted name identifies this component’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

singleton(component_id_spec, parent=None)

Return a singleton Component builder for a component identified by component_id_spec.

Parameters:

• component_id_spec – a context-unique identifier for this component; or the object whose dotted name will identify this component
• parent – the context-unique identifier for this component’s parent template or component definition; or the object whose dotted name identifies this component’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

template(template_id_spec, parent=None)

Return a Template builder for a template identified by template_spec.

Parameters:

• template_id_spec – a context-unique identifier for this template; or the object whose dotted name will identify this template
• parent – the context-unique identifier for this template’s parent template or component definition; or the object whose dotted name identifies this template’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

weakref(component_id_spec, parent=None)

Return a weakref Component builder for a component identified by component_id_spec.

Parameters:

• component_id_spec – a context-unique identifier for this component; or the object whose dotted name will identify this component
• parent – the context-unique identifier for this component’s parent template or component definition; or the object whose dotted name identifies this component’s parent definition

New in version 3.0.0: This method is an entry point into The Aglyph Context fluent API.

class aglyph.context.XMLContext(source, parser=None, default_encoding='ascii')

Bases: aglyph.context.Context

A mapping of unique IDs to Component and Template objects.

Components and templates are declared in an XML document that conforms to the Aglyph context DTD (included in the resources/ directory of the distribution).

Parameters:

• source – a filename or stream from which XML data is read
• parser (xml.etree.ElementTree.XMLParser) – the ElementTree parser to use (instead of Aglyph’s default)
• default_encoding (str) – the default character set used to encode certain element content

Raises:

AglyphError – if unexpected elements are encountered, or if expected elements are not encountered, in the document structure

In most cases, parser should be left unspecified. Aglyph’s default parser will be sufficient for all but extreme edge cases.

default_encoding is the character set used to encode <bytes> (or <str> under Python 2) element content when an @encoding attribute is not specified on those elements. It defaults to the system-dependent value of sys.getdefaultencoding(). This is not related to the document encoding!

Note

Aglyph uses a non-validating XML parser by default, so DTD conformance is not enforced at runtime. It is recommended that XML contexts be validated at least once (manually) during testing.

An AglyphError will be raised under certain conditions (an unexpected element is encounted, or an expected element is not encountered), but Aglyph does not “reinvent the wheel” by implementing strict validation in the parsing logic.

Warning

Although Aglyph contexts are dict types, XMLContext does not permit the same unique ID to be (re-)mapped multiple times.

Attempting to define more than one <component> or <template> with the same ID will raise AglyphError when the document is parsed.

After an Aglyph <context> document has been successfully parsed, a unique component or template ID can be re-mapped using standard dict protocols.

See also

Validity constraint: ID

https://www.w3.org/TR/REC-xml/#id

default_encoding

The default encoding of <bytes> (or <str> under Python 2) element content when an @encoding attribute is not specified.

Note

This is unrelated to the document encoding!