CODEWITHSUNDEEP
robotframework
Joao Coelho
Joao Coelho

Reputation: 3156

Import Python class that only has `__new__` into Robot Framework

Have a python class that is imported in Robot Framework as follows:

Python: MyClass.py

class MyClass:
    def __new__(cls, a, b):
        # implementation here

Robot Framework: MyTest.robot

*** Settings ***
Library    MyClass.py    a=1    b=2

Getting the error Error in file 'MyTest.robot': Test Library 'MyClass' expected 0 arguments, got 2.

I understand the error is because MyClass doesn't have __init__ defined (if it's defined, there's no import error).

My question is: How can I import MyClass.py, which has __new__ defined but not __init__?

(without going into the details of why I have __new__ and not __init__)

Upvotes: 0

Views: 365

Answers (2)

Bryan Oakley
Bryan Oakley

Reputation: 385910

According to the python documentation, __new__ will pass the arguments it receives on to the __init__. Since you didn't create an __init__ that accepts arguments, that's why you get the error.

If __new__() returns an instance of cls, then the new instance’s __init__() method will be invoked like __init__(self[, ...]), where self is the new instance and the remaining arguments are the same as were passed to __new__().

If you don't want the __init__ to be called, you might get some help from this question: Possible to prevent init from being called?

Upvotes: 1

gachdavit
gachdavit

Reputation: 1261

__new__ is responsible on instance creation, and __init__ is just initializer after instance is created. First always is called __new__ and then __init__. __new__ is always @staticmethod as a default, but you can use @staticmethod decorator also (same).

class Foo:

    @staticmethod
    def __new__(cls):
        print('Foo.__new__ is called')
        obj = super().__new__(cls)
        print(obj) # <__main__.Foo object at 0x7f82c1403588> This is "f" object.
        return obj

    def __init__(self, *args, **kwargs):
        print('Foo.__init__ is called !!!')

f = Foo()

Hope, it helps you.

Upvotes: 1

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