[Python] subclassing Q_ in pint - why does the super call not take arguments?

(Python 3.7)

pint / Q_ behavior

I want to subclass pint's quantity class and override __init__. The standard syntax fails because apparently the arguments bubble up to the object init method (which takes no argument):

# file: test.py
from pint import UnitRegistry

ureg = UnitRegistry()
Q_ = ureg.Quantity

class Q_Child_(Q_):
def __init__(self, *args, **kwargs):
super(Q_, self).__init__(*args, **kwargs)
self.foo = 'foo'

a=Q_Child_(1.0, 's') # Raises an error:
# Traceback(most recent call last):
# File ".../test.py", line 12, in < module >
# a = Q_Child_(1.0, 's')
# File ".../test.py", line 9, in __init__
# super(Q_, self).__init__(*args, **kwargs)
# TypeError: object.__init__() takes exactly one argument(the instance to initialize)


What seems to work is to not call super/init at all in the subclassing, but how does this even make sense?

from pint import UnitRegistry

ureg = UnitRegistry()
Q_ = ureg.Quantity

class Q_Child_(Q_):
def __init__(self, *args, **kwargs):
# not calling super or Q_.__init__ (or so it seems)
self.foo = 'foo'

a=Q_Child_(1.0, 's')
print(a) # '1.0 second' -> how does it even know the passed arguments?
print(a.foo) # 'foo'


I believe the latter is what I want to use, but using code that works when you think it should not work seems a recipe for disaster. What is happening?

I guess it is due to Q_ being generated dynamically (when ureg is instantiated, see https://github.com/hgrecco/pint/blob/master/pint/registry.py#L115 and https://github.com/hgrecco/pint/blob/master/pint/quantity.py#L1741) but fail to see why it should matter.

That question is not a duplicate of correct way to use super (argument passing) (or similar) because the standard way does not work here:

class NewDict(dict):
def __init__(self, *args, foo='foo', **kwargs):
super(NewDict, self).__init__(*args, **kwargs)
self.foo = foo

nd = NewDict({'a': 1}, foo='bar')
print(nd) # {'a': 1}
print(nd.foo) # 'bar'


Without the super call, the parent class has no way to know the arguments that it is supposed to initialize with:

class NewDictWithoutSuper(dict):
def __init__(self, *args, foo='foo', **kwargs):
self.foo = foo

nd = NewDictWithoutSuper({'a': 1}, foo='bar')
print(nd) # {} i.e. the default dict()
print(nd.foo) # 'bar'

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