How to import and use user defined classes in robot framework with python

I have been able to instantiate python classes on-demand (i.e. not just hard-coded args as via the Library technique).

I used a helper method to create the class. I was unable to get the Robot script to call the class constructor directly, however it is able to call functions in Python, so we can create a class or namedtuple by providing a function-based interface:

File: resource_MakeMyClass.robot

*** Settings ***
Library             myClass

*** Keywords ***
_MakeMyClass
    [Arguments]    ${arg1}    ${arg2}
    ${result} =    makeMyClass    ${arg1}    ${arg2}
    [Return]       ${result}

File: myClass.py

class MyClass(object):
    def __init__(self, arg1, arg2):
        self.arg1 = arg1
        self.arg2 = arg2

def makeMyClass(arg1, arg2):
    return MyClass(arg1, arg2)

To import the library with arguments, just add them after the library name:

Library  TestClass  ARG1  ARG2

So the "import" and the instantiation are done in one shot. Now, the thing that can be tricky is to understand the scope of your instance. This is well explained in the User Guide section "Test Library Scope":

A new instance is created for every test case. [...] This is the default.

Note that if you want to import the same library several times with different arguments, and hence have difference instances of your classes, you will have to name them on import:

Library  TestClass  ARG1  ARG2  WITH NAME  First_lib
Library  TestClass  ARG3  ARG4  WITH NAME  Second_lib

And then in your tests, you have to prefix the keywords:

*** Test Cases ***
MyTest
    First_lib.mykeyword  foo  bar
    Second_lib.mykeyword  john  doe

This is explained in this section of the User Guide.