Last-session aware class

last-session-aware-class.py

"""
A proof of concept: ability to have `X.f(...) == X.sess.f(...)`, but also be
able to use `x = X(); y = X(); x.f(...)` in the expected way.
"""

import inspect


class _X:
    """
    We put properties and instance methods here.
    """

    sess = None

    def __init__(self, foo):
        type(self).sess = self
        self.foo = foo

    def f(self, X=None):
        print(self, X)


class _meta_x(type):
    def __new__(cls, *args, **kwargs):
        for name, f in inspect.getmembers(_X, predicate=inspect.isfunction):
            if not name.startswith("_"):
                setattr(cls, name, cls.__session_method(f))
        return super().__new__(cls, *args, **kwargs)

    def __session_method(f):
        def wrapped(cls, *args, **kwargs):
            f(_X.sess, *args, **kwargs)
        return wrapped


class X(object, metaclass=_meta_x):
    """
    We want to use this class.
    """

    def __new__(cls, *args, **kwargs):
        return _X(*args, **kwargs)


print("1: ", end=""); X.f()
print("2: ", end=""); X.f(17)
print("3: ", end=""); X(1).f()
print("4: ", end=""); X(1).f(17)
print("5: ", end=""); X.f()
print("6: ", end=""); X.f(17)

# Careful: the type is not what the constructor would imply!
print(type(X(1)), "!=", X)