Where is the function is_return defined?

Frappe Framework Custom Script
1

I see a lot of reference to this self.is_return in Python script but I cannot see where this function is defined. I can’t find def is_return. Can someone please tell me where this function is defined ?

2

@The_Lowkster
is_return is not a function it is check box in DocType
e.g. Delivery Note DocType

Screenshot from 2016-06-03 17:01:02.png1028×705 41.4 KB

3

Ah! Okay. Thanks!!