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A property getter in Python is a method accessed via standard attribute syntax, abstracting method invocation behind attribute retrieval. It is implemented using the @property decorator, which transforms the decorated method into a read-only descriptor by binding it to the fget parameter of the built-in property class. When the Python interpreter encounters attribute access for a property, it invokes the descriptor protocol’s __get__ method, which in turn executes the underlying getter function and returns its result.

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Syntax and Implementation

The standard and most idiomatic approach utilizes the @property decorator. The name of the method becomes the name of the exposed attribute. 
class Entity:
    def __init__(self, value):
        self._internal_state = value

    @property
    def state(self):
        return self._internal_state

obj = Entity(42)

# The getter is invoked without parentheses via attribute access syntax
print(obj.state)  # Output: 42

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The property() Built-in

Under the hood, @property is syntactic sugar for the property() built-in function. The signature for this built-in is: 
property(fget=None, fset=None, fdel=None, doc=None)
When used as a decorator, the method immediately following @property is passed as the fget argument. The equivalent non-decorator implementation demonstrates this binding explicitly: 
class Entity:
    def __init__(self, value):
        self._internal_state = value

    def get_state(self):
        return self._internal_state

    # Explicitly binding the getter method to the fget parameter
    state = property(fget=get_state)

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Descriptor Protocol Mechanics

Because property implements the descriptor protocol, accessing the attribute triggers the __get__(self, obj, objtype=None) method of the property object. When obj.state is evaluated:
  1. Python checks the class dictionary (Entity.__dict__) for the state attribute.
  2. It identifies state as a descriptor (a property object).
  3. It executes Entity.__dict__['state'].__get__(obj, Entity).
  4. The __get__ method executes the bound fget function (the decorated method) and returns the computed value.
Attempting to assign a value to a property that only has an fget defined will raise an AttributeError, as the absence of an fset binding enforces read-only behavior at the descriptor level.
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