passing arguments to a function using kwargs - Python

Question

I have the following code snippet:

kwargs = {'inventory_file' : self.inventory_file}
for ts in self.test_sets_list:
   current_ts = TestSet(name=ts,
                        test_cases=self.test_sets_list[ts],
                        om_ip_address=self.om_ip_address,
                        **kwargs)


class TestSet(object):
   def __init__(self, name, test_cases, om_ip_address, **kwargs):


class TestCase(object):
        def __init__(self, parameters, config_file, test_failure,
                 om_ip_address, **kwargs):

I know I'm probably doing wrong, because in **kwargs I'm unpacking the values in kwargs . What I want is to pass the arguments of kwargs all the way to TestCase . Inside TestSet I'm trying to pass the kwargs argument:

instance = TestCase(parameters=params, 
                    config_file=cnf,
                    om_ip_address=om_ip_address,
                    **kwargs)

However I'm getting the following error:

Traceback (most recent call last):
  File "main.py", line 258, in <module>
    main(args)
  File "main.py", line 217, in main
    operation.collect_tests()
  File "main.py", line 157, in collect_tests
    **kwargs)
  File "test_set.py", line 47, in __init__
    self.__instantiate_module(tc, om_ip_address)
  File "test_set.py", line 78, in __instantiate_module
    **self.kwargs)
TypeError: __init__() got an unexpected keyword argument 'inventory_file

The class is instantiated via:

    my_class = getattr(module, test_cases['name'])
    instance = my_class(parameters=params, 
                        config_file=cnf,
                        om_ip_address=om_ip_address)

How can I be able to pass kwargs all the way to TestCase ?

Answer 1

Calling a function with **kwargs , where kwargs = {'inventory_file' : self.inventory_file} is the same as calling

function(inventory_file=self.inventory_file)

and if the definition of function doesn't have inventory_file in the accepted params list, it will throw the error you got there. Two ways to solve this:

class TestCase(object):
    # add inventory_file to the params list with a default value
    def __init__(self, parameters, config_file, test_failure,
             om_ip_address, inventory_file=None, **kwargs):
        self.inventory_file = inventory_file

or:

class TestCase(object):
    # check for the inventory file in the kwargs dict
    def __init__(self, parameters, config_file, test_failure,
             om_ip_address, **kwargs):
        if 'inventory_file' in kwargs:
             self.inventory_file = kwargs['inventory_file']

and in both cases:

>>> t = TestCase('param1','param2','param3','param4', **{'inventory_file':'file'})
>>> t.inventory_file
'file'