I found the very usefull nullable or non-nullable arguments script on stackoverflow - https://stackoverflow.com/a/53639511. This guy also created a repository with his script: https://github.com/unitedsoftwork/python-not-none. I wanted to use it, but it didn't work with **kwargs. As I am using keyword arguments nearly every time I edited his scr…

nullable_decorator.py

def not_none(nullable_parameters=None):
  # values given by real_decorator (see below)
  def the_actual_test(f, expected_args_with_given, allowed_nullable_args):
    has_none = False
    bad_parameters = []

    for key, value in expected_args_with_given.items():
      if (value is None and nullable_parameters is None) or \
              (value is None and key not in nullable_parameters):
        bad_parameters.append(key)
        has_none = True

    if has_none:
      raise ValueError("[Function '{}' of '{}'] - IMPORTANT: Parameters '{}' cannot be None. ".format(f.__name__, f.__module__, bad_parameters))

  # here the code REALLY begins
  def not_null_decorator(original_func):
    import inspect
    has_self = False
    # f.__code__.co_varnames --> local variables (not only parameters), see: https://python-reference.readthedocs.io/en/latest/docs/code/varnames.html
    # get declared arguments from ogirinal function
    argspec = inspect.getargspec(original_func)
    if 'self' in argspec.args:
      argnames = argspec.args[1:]  # no self
      has_self = True
    else:
      argnames = argspec.args
    args_dict = dict.fromkeys(argnames)

    def get_args(*args, **kwargs):
      for arg in args:
        if arg in args_dict.keys():
          args_dict[arg] = arg
      for key, value in kwargs.items():
        if key in args_dict.keys():
          args_dict[key] = value

      return args_dict

    def wrapper_with_self(self, *args, **kwargs):
      the_actual_test(original_func, get_args(*args, **kwargs), nullable_parameters)
      return original_func(self, *args, **kwargs)

    def wrapper(*args, **kwargs):
      the_actual_test(original_func, get_args(*args, **kwargs), nullable_parameters)
      return original_func(*args, **kwargs)

    if has_self:
      return wrapper_with_self
    else:
      return wrapper

  return not_null_decorator


############################
# usage:
# from .nullable_decorator import not_none
#
# @not_none(nullable_parameters=["nullable_arg1", "nullable_arg2"])
# def some_function(self, nullable_arg1=None, nullable_arg2=None, non_nullable_arg1=None):
#   pass
#
# @not_none()
# def some_other_function(self, non_nullable_arg1=None, non_nullable_arg2=None):
#   pass