micropython/tests/basics/object_new.py

# object.__new__(cls) is the only way in Python to allocate empty
# (non-initialized) instance of class.
# See e.g. http://infohost.nmt.edu/tcc/help/pubs/python/web/new-new-method.html
# TODO: Find reference in CPython docs
try:
    # If we don't expose object.__new__ (small ports), there's
    # nothing to test.
    object.__new__
except AttributeError:
    print("SKIP")
    raise SystemExit

class Foo:

    def __new__(cls):
        # Should not be called in this test
        print("in __new__")
        raise RuntimeError

    def __init__(self):
        print("in __init__")
        self.attr = "something"


o = object.__new__(Foo)
#print(o)
print("Result of __new__ has .attr:", hasattr(o, "attr"))
print("Result of __new__ is already a Foo:", isinstance(o, Foo))

o.__init__()
#print(dir(o))
print("After __init__ has .attr:", hasattr(o, "attr"))
print(".attr:", o.attr)

# should only be able to call __new__ on user types
try:
    object.__new__(1)
except TypeError:
    print("TypeError")
try:
    object.__new__(int)
except TypeError:
    print("TypeError")