Python how to get __qualname__ of method wrapped with property.setter

Question

I have an instance attribute that I made a property using Python's property decorator.

I then made a setter for the property using the decorator @property_name.setter.

How can I get the __qualname__ of the original method definition, decorated with @property.setter?

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Where I Have Looked

• Python: __qualname__ of function with decorator
  • I don't think property uses @functools.wraps()
• Python @property.setter
  • I realize property is actually a descriptor
• Decorating a class method after @property
  • Tells me I may want to use __get__, but I can't figure out the syntax

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Example Code

This was written in Python 3.6.

#!/usr/bin/env python3


def print_qualname():
    """Wraps a method, printing its qualified name."""

    def print_qualname_decorator(func):
        # print(f"func = {func} and dir(): {dir(func)}")
        if hasattr(func, "__qualname__"):
            print(f"Qualified name = {func.__qualname__}.")
        else:
            print("Doesn't have qualified name.")

    return print_qualname_decorator


class SomeClass:

    def __init__(self):
        self._some_attr = 0
        self._another_attr = 0

    @property
    def some_attr(self) -> int:
        return self._some_attr

    @print_qualname()
    @some_attr.setter
    def some_attr(self, val: int) -> None:
        self._some_attr = val

    @print_qualname()
    def get_another_attr(self) -> int:
        return self._another_attr

Output:

Doesn't have qualified name.
Qualified name = SomeClass.get_another_attr.

How can I get the __qualname__ for some_attr from inside the print_qualname decorator? In other words, how do I get SomeClass.some_attr to be output?

Answer 1

You could flip the ordering of the decorators for the setter. Note I've adjusted the print_qualname_decorator to call the underlying function and return it (otherwise the setter will not execute).

from functools import wraps

def print_qualname(func):
    """Wraps a method, printing its qualified name."""
    @wraps(func)
    def print_qualname_decorator(*args):
        if hasattr(func, "__qualname__"):
            print(f"Qualified name = {func.__qualname__}.")
        else:
            print("Doesn't have qualified name.")
        return func(*args)
    return print_qualname_decorator


class SomeClass:

    def __init__(self):
        self._some_attr = 0
        self._another_attr = 0

    @property
    def some_attr(self) -> int:
        return self._some_attr

    @some_attr.setter
    @print_qualname
    def some_attr(self, val: int) -> None:
        self._some_attr = val

    @print_qualname
    def get_another_attr(self) -> int:
        return self._another_attr

Use

In [46]: foo = SomeClass()                                               

In [47]: foo.get_another_attr()                                          
Qualified name = SomeClass.get_another_attr.
Out[47]: 0

In [48]: foo.some_attr = 5                                               
Qualified name = SomeClass.some_attr.

In [49]: foo._some_attr                                                  
Out[49]: 5