Proposal: private keyword for import statements to hide module dependencies

Hi, this is my first time here on the mailing list. 

I would like to open up for a discussion on how we can introduce a way to hide imports.
I am proposing the introduction of an optional, non-breaking keyword, private, to be used when importing a file. The goal is to allow developer to hide internal dependencies and  prevent them from leaking into the module's public namespace.

Under the current system, any object imported into a module's top-level scope becomes an accessible attribute of that module.
module/math.py
'''
import numpy as np

def calculate_mean(data: np.ndarray) -> float:
    return np.mean(data)
'''
The issue is that when a user imports this module, the import is exposed.
'''
import module.math
# This is valid, even though 'np' is an internal detail:
# module.math.np
'''

While we have some conventions, we do not have explicit hiding of such modules. 
We have one solution, which is more like a convention

'''
import numpy as _np

'''
This hides it for common usage and signals to the developer that it is private.

__all__ works for wildcard imports, but not for standard imports. 

I suggest adopting a solution similar to what has been implemented in swift, which is to introduce a modifier keyword:
'''
private import numpy as np

def calculate_mean(data: np.ndarray) -> float:
    return np.mean(data)

'''

Internally in the file np is accesible, but when importing the file it is not accesible.

Expected behaviour:

import module.math	
module.math.np
This  raises an AttributeError

from module.math import np	raises an ImportError

from module.math import calculate_mean	Succeeds