kadet

Easily define and reuse complex Python objects that serialize into JSON or YAML.

Example

from kadet import BaseObj
from pprint import pprint

ships = BaseObj()
ships.root.type.container = ["panamax", "suezmax", "post-panamax"]
ships.root.type.carrier = ["conventional", "geared", "gearless"]
ships.root.type.tanker = BaseObj.from_yaml("tankers.yml")

pprint(ships.root)

# output
{'type': {'carrier': ['conventional',
                      'geared',
                      'gearless'],
          'container': ['panamax',
                        'suezmax',
                        'post-panamax'],
          'tanker': ['oil', 'liquified-gas', 'chemical']}}

Installation

Install using pip install kadet.

Overview

BaseObj

BaseObj implements the basic object that serializes into JSON or YAML. Setting keys in self.root means they will be serialized. Keys can be set as an hierarchy of attributes.

The self.body() method is reserved for setting self.root on instantiation.

The example below:

class MyApp(BaseObj):
  def body(self):
    self.root.name = "myapp"
    self.root.inner.foo = "bar"
    self.root.list = [1, 2, 3]

yaml.dump(MyApp().dump())

serializes into:

---
name: myapp
inner:
  foo: bar
list:
  - 1
  - 2
  - 3

The self.new() method can be used to define a basic constructor.

self.need() checks if a key is set and errors if it isn't (with an optional custom error message). self.optional() sets a key as optional. Use default keyword to set default value when not set.

Both self.new() and self.body() method accept the istype keyword to validate value type on runtime. Supports typing types.

kwargs that are passed onto a new instance of BaseObj are always accessible via self.kwargs

self.new_with() is an utility method to call super().new() while passing kwargs to the super class.

In this example, MyApp needs name and foo to be passed as kwargs.

class MyApp(BaseObj):
  def new(self):
    self.need("name")
    self.need("foo", msg="please provide a value for foo")
    self.optional("baz")

  def body(self):
    self.root.name = self.kwargs.name
    self.root.inner.foo = self.kwargs.foo
    self.root.list = [1, 2, 3]

obj = MyApp(name="myapp", foo="bar")

Setting a skeleton

Defining a large body with Python can be quite hard and repetitive to read and write.

The self.root_file() method allows importing a YAML/JSON file to set self.root.

MyApp's skeleton can be set instead like this:

#skel.yml
---
name: myapp
inner:
  foo: bar
list:
  - 1
  - 2
  - 3

class MyApp(BaseObj):
  def new(self):
    self.need("name")
    self.need("foo", msg="please provide a value for foo")
    self.root_file("path/to/skel.yml")

Extending a MyApp's skeleton is possible just by implementing self.body():

class MyApp(BaseObj):
  def new(self):
    self.need("name")
    self.need("foo", msg="please provide a value for foo")
    self.root_file("path/to/skel.yml")

  def body(self):
    self.set_replicas()
    self.root.metadata.labels = {"app": "mylabel"}

  def set_replicas(self):
    self.root.spec.replicas = 5

Inheritance

Python inheritance will work as expected:

class MyOtherApp(MyApp):
  def new(self):
    super().new()  # MyApp's new()
    self.need("size")

  def body(self):
    super().body()  #  we want to extend MyApp's body
    self.root.size = self.kwargs.size
    del self.root.list  # get rid of "list"

obj = MyOtherApp(name="otherapp1", foo="bar2", size=3)
yaml.dump(obj.dump())

serializes to:

---
name: otherapp1
inner:
  foo: bar2
replicas: 5
size: 3

BaseModel

BaseModel integrates Kadet semantics with Pydantic's BaseModel together with powerful data validation and type hinting features. Just like in BaseObj, keys in self.root will be serialized, but kwargs is no longer necessary as BaseModel's parameters are set as attributes in self.

The self.body() method is reserved for setting self.root on instantiation.

The example below:

class Boat(BaseModel):
  name: str  # Required
  length: int  # Required
  description: str = "I am a boat"  # Default description

  def body(self):
    self.root.name = self.name
    self.root.details.length = self.length
    self.root.details.description = self.description

print(yaml.dump(Boat(name="Boaty", length=600).dump()))

---
details:
  description: I am a boat
  length: 600
name: Boaty