can I regard __slots__ as the __all__ for classes?

Question

Noticing they both limit the things that can be called from outside.

__all__ = [
    'Point',
]

class Point(object):
    __slots__ = ('x', 'y')

    def __init__(self, x, y):
        self.x = x
        self.y = y

Answer 1

__all__ only affects starred imports - only names from __all__ will be imported after doing from mymodule import * (if __all__ is present, of course). You can still access names not listed there:

In [4]: import mymodule

In [5]: mymodule.__all__
Out[5]: ['a']

In [6]: mymodule.b
Out[6]: 'was not in __all__'

__slots__ prevents the __dict__ attribute from being created (restricting the ability to set arbitrary attributes to instances of certain class):

In [10]: class A():
   ...:     __slots__ = ('a',)
   ...:     

In [11]: a = A()

In [12]: a.b = 'was not in __slots__'
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-3-fb77d7bc2a79> in <module>()
----> 1 a.b = 'was not in __slots__'

AttributeError: 'A' object has no attribute 'b'

These are 2 different things.