Declarative Python meta-model system and visitor utilities
Project description
The normalize package is a class builder and toolkit most useful for writing “plain old data structures” to wrap data from network sources in python objects.
It is called “normalize”, because it is focused on the first normal form of relational database modelling. This is the simplest and most straightforward level which defines what are normally called “records” (or rows). A record is a defined collection of properties/attributes (columns), where you know roughly what to expect in each property/attribute, and can access them by some kind of descriptor (i.e., the attribute name). You can also use it as a general purpose declarative meta-programming framework, as it ships with an official meta-object-protocol (MOP) API to describe this information, built on top of python’s notion of classes/types and descriptors and extended where necessary.
Put simply, you write python classes to describe your assumptions about the data structures you’re dealing with, feed in input data and you get regular python objects back which have attributes which you can use naturally. Or, you get an error and find you have to revisit your assumptions. You can then perform basic operations with the objects, such as make changes to them and convert them back, or compare them to another version using the rich comparison API. You can also construct the objects ‘natively’ using regular python keyword/value constructors or by passing a dict as the first argument.
It is very similar in scope to the remoteobjects and schematics packages on PyPI, and may in time evolve to include all the features of those packages.
While there is some notion of primary keys in the module, mainly for the purposes of recognizing objects in collections for comparison, higher levels of normalization are an exercise left to the implementer.
Features
declarative API, which may optionally contain direct marshaling hints:
class Star(Record): id = Property(isa=int, required=True) name = Property(isa=str) other_names = Property(json_name="otherNames")Type descriptions (isa=) are completely optional, but if given will be use for type checking and coercion.
rich descriptor API (in normalize.property), including the notions of not just ‘required’ and ‘isa’ type hints as shown above but also default functions, custom-type check functions, and coercion functions.
It also sports an extensible attribute trait system, which adds more features via optional Property sub-classes, selected automatically, enabling:
lazy attributes which short-cut at the python core level once calculated (a somewhat underused python feature)
read-only attributes
type-safe attributes (i.e., that type-check on assign)
collection attributes (see below)
coercion from regular python dictionaries or key=value (kwargs) constructor arguments
conversion to and from JSON for all classes, regardless of whether they derive normalize.record.json.JsonRecord, using the visitor pattern. Support for custom functions for JSON marshal in and out.
conversion to primitive python types via the pickle API (__getnewargs__)
New in 0.5: generic mechanism for marshalling to and from other other forms. See the documentation for the new normalize.visitor.VisitorPattern API.
typed collections API with item coercion (currently, only lists are implemented):
class StarSystem(Record): components = ListProperty(Star) alpha_centauri = StarSystem( components=[{id=70890, name="Proxima Centauri"}, {id=71683, name="Alpha Centauri A"}, {id=71681, name="Alpha Centauri B"}] )“field selector” API which allows for specification of properties deep into nested data structures;
name_selector = FieldSelector("components", 0, "name") print name_selector.get(alpha_centauri) # "Proxima Centauri"comparison API which returns differences between two Records of matching types. Ability to mark properties as “extraneous” to skip comparison (this also affects the == operator)
…and much more!
Release history Release notifications | RSS feed
Download files
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.
