[Python] Django built-in class based view - Where is self.object from?

In the following code, I don't understand something about the object.

class SingleObjectMixin(ContextMixin):
"""
Provide the ability to retrieve a single object for further manipulation.
"""
model = None
queryset = None
slug_field = 'slug'
context_object_name = None
slug_url_kwarg = 'slug'
pk_url_kwarg = 'pk'
query_pk_and_slug = False

...

...


def get_context_data(self, **kwargs):
"""Insert the single object into the context dict."""
context = {}
if self.object:
context['object'] = self.object
context_object_name = self.get_context_object_name(self.object)
if context_object_name:
context[context_object_name] = self.object
context.update(kwargs)
return super().get_context_data(**context)


There is an attribute self.object in the method get_context_data. I would like to figure out where the attribute object is created from.

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