Each Answer to this Q is separated by one/two green lines.
This is inspired by a question I just saw, “Change what is returned by calling class instance”, but was quickly answered with
__repr__ (and accepted, so the questioner did not actually intend to call the instance).
Now calling an instance of a class can be done like this:
instance_of_object = object() instance_of_object()
but we’ll get an error, something like
TypeError: 'object' object is not callable.
This behavior is defined in the CPython source here.
So to ensure we have this question on Stackoverflow:
How do you actually call an instance of a class in Python?
You call an instance of a class as in the following:
o = object() # create our instance o() # call the instance
But this will typically give us an error.
Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'object' object is not callable
How can we call the instance as intended, and perhaps get something useful out of it?
We have to implement Python special method,
class Knight(object): def __call__(self, foo, bar, baz=None): print(foo) print(bar) print(bar) print(bar) print(baz)
Instantiate the class:
a_knight = Knight()
Now we can call the class instance:
a_knight('ni!', 'ichi', 'pitang-zoom-boing!')
ni! ichi ichi ichi pitang-zoom-boing!
And we have now actually, and successfully, called an instance of the class!
The short answer is that the
object class has no
__call__ method (you can check that with “dir(object)”). When you create an instance of a class the
__init__ method is called and when you call the instance, the
__call__ method is called.
Up Votes for Everyone!
Thanks for posting the question and thanks for answering.
I thought I would just share my implementation in case that helps others …
I have a class (called RTS) and it contains an SQL Query that I access using a ‘get’. The class works fine as an independent endpoint. Now I want to call that class from within the program.
Using the answer above I added the following:
class RTS(Resource): def __call__(self): print("In RTS") def get(self, user_id): try: ...
In order to call the class from elsewhere in the program I added:
getGR = RTS.get(self, user_unique_id)
Voila – I got the same info I could check on Postman returned within the program.