How can I import LambdaContext?

Question

I'm making AWS Lambda Function. Now I want to isinstance(context,LambdaContext) , I'm expecting It works in AWS Lambda. But I'm running unit test in local.

So How can I import LambdaContext.

Best

Answer 1

Just found this package, it seems that someone made a pip package using the concepts from the other answers in this question.

Had the same issue, hope it helps whoever comes across this question in the future.

Answer 2

This is not in the strictest sense an answer, please remove if unsuitable.

I have experimented with @Dmitry-Masanov 's answer, and have bodged a python fixture for pytest, which can be used either in the test script itself, or as I am doing, in the conftest.py file.

@pytest.fixture
def mock_lambda_context():
    class ClientContext:
        """
        Class for mocking Context

        Has `custom`, `env`, and `client` `__slots__`
        """

        __slots__ = ["custom", "env", "client"]

    def make_obj_from_dict(_class, _dict, fields=None):
        """
        Makes an object of `_class` from a `dict`

        :param _class: A class representing the context
        :type _class: `ContextClass`
        :param _dict: A dictionary of data 
        :type _dict: `dict`
        :param fields: [description], defaults to None
        :type fields: [type], optional
        :return: An object
        :rtype: `ClientContext` class
        """
        if _dict is None:
            return None
        obj = _class()
        set_obj_from_dict(obj, _dict)
        return obj

    def set_obj_from_dict(obj, _dict, fields=None):
        if fields is None:
            fields = obj.__class__.__slots__
        for field in fields:
            setattr(obj, field, _dict.get(field, None))

    class LambdaContext(object):
        """
        Create a Lambda Context Class object
        """

        def __init__(self, invokeid, client_context, invoked_function_arn=None):
            self.aws_request_id = invokeid
            self.log_group_name = "AWS_LAMBDA_LOG_GROUP_NAME"
            self.log_stream_name = "AWS_LAMBDA_LOG_STREAM_NAME"
            self.function_name = "AWS_LAMBDA_FUNCTION_NAME"
            self.memory_limit_in_mb = "AWS_LAMBDA_FUNCTION_MEMORY_SIZE"
            self.function_version = "AWS_LAMBDA_FUNCTION_VERSION"
            self.invoked_function_arn = invoked_function_arn

            self.client_context = make_obj_from_dict(ClientContext, client_context)
            if self.client_context is not None:
                self.client_context.client = None
            self.identity = None

        def get_remaining_time_in_millis(self):
            return None

        def log(self, msg):
            str_msg = str(msg)
            print(str_msg)

    lambda_context = LambdaContext("AWS_ID", {})

    return lambda_context

I'm nearly certain my implementation can be improved (OO python isn't a strong skill of mine), but this serves my purpose of:

• mocking a lambda context object
• integrating with pytest

This can be used in a way similar to this:

@pytest.mark.smoke
def test_lambda_handler(apigw_event, mock_lambda_context):
    ret = app.lambda_handler(apigw_event, mock_lambda_context)
    assert "log_stream_name" in ret["body"]

Thanks again Dmitry, your answer saved me a bunch of hassle.