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# Python Property Getter
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.
## 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.
```python theme={"dark"}
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
```
## The `property()` Built-in
Under the hood, `@property` is syntactic sugar for the `property()` built-in function. The signature for this built-in is:
```python theme={"dark"}
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:
```python theme={"dark"}
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)
```
## 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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