Move regular expression compilation to the top of the module in create_from_yaml

I was going through the codebase and was trying to understand it. I landed up at:

https://github.com/kubernetes-client/python/blob/6d64cf67d38337a6fdde1908bdadf047b7118731/kubernetes/utils/create_from_yaml.py#L142-L178

I think we can refactor this function by breaking down it into a couple of nested functions to reduce cognitive complexity and maybe distribute responsibilities.

Furthermore, I have this suggestion and would love to contribute if such a change is acceptable.

upper_followed_by_lower_re = re.compile('(.)([A-Z][a-z]+)')
lower_or_num_followed_by_upper_re = re.compile('([a-z0-9])([A-Z])')

def create_from_yaml_single_item(
        k8s_client, yml_object, verbose=False, **kwargs):

    def get_version_and_group(_api_version):
        _group, _, _version = _api_version.partition("/")
        if _version == "":
            _version = group
            _group = "core"
        return _version, _group

    def clean_group(_group):
        # Take care for the case e.g. api_type is "apiextensions.k8s.io"
        # Only replace the last instance
        _group = "".join(_group.rsplit(".k8s.io", 1))
        # convert group name from DNS subdomain format to
        # python class name convention
        return "".join(word.capitalize() for word in _group.split('.'))

    def clean_kind(_kind):
        # Replace CamelCased action_type into snake_case
        _kind = upper_followed_by_lower_re.sub(r'\1_\2', _kind)
        return lower_or_num_followed_by_upper_re.sub(r'\1_\2', _kind).lower()

    def get_response(_yml_obj, _k8s_api, _kind, **_kwargs):

        def get_namespaced_response(__yml_obj, __k8s_api, __kind, **__kwargs):
            __namespace = __yml_obj["metadata"]["namespace"]
            __kwargs['namespace'] = __namespace
            return getattr(__k8s_api, "create_namespaced_{0}".format(_kind_))(
                body=__yml_obj, **__kwargs)

        def get_non_namespaced_response(__yml_obj, __k8s_apis, __kind, **__kwargs):
            __kwargs.pop('namespace', None)
            return getattr(__k8s_api, "create_{0}".format(__kind))(
                body=__yml_obj, **__kwargs)

        # Expect the user to create namespaced objects more often
        if hasattr(_k8s_api, "create_namespaced_{0}"._format(kind)):
            # Decide which namespace we are going to put the object in,
            # if any
            return get_namespaced_response(_yml_obj, _k8s_api, _kind, **_kwargs)
        return get_non_namespaced_response(_yml_obj, _k8s_api, _kind, **_kwargs)


    def display_message(_kind, _resp, *, _verbose):
        if _verbose:
            _msg = "{0} created.".format(_kind)
            if hasattr(resp, 'status'):
                _msg += " status='{0}'".format(str(_resp.status))
            print(_msg)


    version, group = get_version_and_group(yml_object['apiVersion'])
    group = clean_group(group)

    fcn_to_call = "{0}{1}Api".format(group, version.capitalize())
    k8s_api = getattr(client, fcn_to_call)(k8s_client)
    kind = clean_kind(yml_object['kind'])
    resp = get_response(yml_object, k8s_api, kind, **kwargs)
    display_message(kind, resp, _verbose=verbose)
    return resp

Regarding the code:

• Prefixed _ in nested function variables so that they are there are lesser chances of facing scoping issues.
• Move the regular expression pattern to the top of the module as it can hopefully reduce execution time.

I believe a couple of other functions too can be broken down but just wanted to confirm if this is acceptable.

[yliaog]

i’m not sure about the backward incompatibility part, we need the community input on whether it’s worthwhile to make the breaking change. Feel free to send out a PR, we can ask the community to weigh in.

[abhiabhi94]

So, if you agree, i can make a separate pull request for removing the boolean-trap, and it can be merged when a major version is upgraded.