Welcome to Atom

from atom.api import Atom, Str, Range, Bool, observe
class Person(Atom):
 """ A simple class representing a person object.

 """
 last_name = Str()
 first_name = Str()
 age = Range(low=0)
 debug = Bool(False)
 @observe('age')
 def debug_print(self, change):
 """ Prints out a debug message whenever the person's age changes.

 """
 if self.debug:
 templ = "{first} {last} is {age} years old."
 s = templ.format(
 first=self.first_name, last=self.last_name, age=self.age,
 )
 print(s)
 def _default_first_name(self):
 return 'John'
john = Person(last_name='Doe', age=42)
john.debug = True
john.age = 43 # prints message
john.age = 'forty three' # raises TypeError

from atom.api import Atom, observe
class InventoryItem(Atom):
 """Class for keeping track of an item in inventory."""
 name: str
 unit_price: float
 quantity_on_hand: int = 0
 def total_cost(self) -> float:
 return self.unit_price * self.quantity_on_hand
 @observe("unit_price")
 def check_for_price_reduction(self, change):
 savings = change.get("oldvalue", 0) - change.get("value")
 if savings > 0:
 print(f"Save ${savings} now on {self.name}s!")
>>> w = InventoryItem(name="widget", unit_price=1.99, quantity_on_hand=10)
>>> w.unit_price = 1.00
Save $0.99 now on widgets!