Is it possible to call a class but without a new instance created?

[Jach Fong]

It seems most of confusion comes from mixing up python object and tk
widgets, and ignored that the tkinter is really a python-tk-interface.
Thank you for pointing it out.


Terry Reedy at 2018/6/18 PM 05:19 wrote:
> To answer the question of the title, which is a bit different from the 
> question in the text, yes.  type(None)() always returns the singleton 
> None object.  (And one can write a singleton class in Python also.) 
> bool() always returns one of False or True.  int() and str() may return 
> either a new or old object.  For such immutables, it does not matter as 
> long at the object has the correct value.  As others said, this is all 
> handled in a __new__ method.  But none of this has much to do with 
> tkinter instances.
> 
> On 6/18/2018 5:09 AM, Terry Reedy wrote:
>> On 6/18/2018 12:48 AM, Jach Fong wrote:
>>> After looking into the \tkiniter\font.py source file, triggered by Jim's
>>> hint on my previous subject "Why an object changes its "address" between
>>> adjacent calls?", I get more confused.
>>>
>>> Below was quoted from the font.py:
>>> ------------------------
>>> def nametofont(name):
>>>      """Given the name of a tk named font, returns a Font 
>>> representation.
>>>      """
>>>      return Font(name=name, exists=True)
>>>
>>> class Font:
>>>      """Represents a named font.
>>
>> tkinter abbreviates tk interface.  A Python tkinter Font instance 
>> represents a tk named font structure. It has a hidden pointer to the 
>> tk structure.  The same is true of all instances of tkinter widgets 
>> classes.  Each has a hidden pointer to a tk widget
>>
>>>      Constructor options are:
>>>      ...
>>>      exists -- does a named font by this name already exist?
>>
>> Does a *tk* named font exist?
>>
>>>         Creates a new named font if False, points to the existing 
>>> font if True.
>>
>> Again, 'font' here means a tk structure, not a python instance.  Each 
>> call to Font returns a new python instance.  But for Fonts, it may or 
>> may not point to a new tk structure.
>>
>>>      ...
>>>      """
>>>
>>>      def __init__(self, root=None, font=None, name=None, exists=False,
>>>                   **options):
>>>          ...
>>
>> One can mostly ignore the parallel existence of python instances and 
>> tk structures.  But they can get out of sync during shutdown.  If t is 
>> an instance of Text, t.destroy() causes tkinter to tell tk to destroy 
>> the tk widget, leaving t useless.  Similarly, if 'del t' deletes the 
>> last reference to the Python instance, it may disappear, leaving the 
>> tk widget possibly unaccessible.
>>
> 
> 

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