If you need access to the internal states of a function, you're possibly better off using a class. You can make a class instance behave like a function by making it a callable, which is done by defining __call__:
class StatefulFunction( object ):
def __init__( self ):
self.public_value = 'foo'
def __call__( self ):
return self.public_value
>> f = StatefulFunction()
>> f()
`foo`
>> f.public_value = 'bar'
>> f()
`bar`