Complete scan of dynamoDb with boto3

Question

My table is around 220mb with 250k records within it. I\'m trying to pull all of this data into python. I realize this needs to be a chunked batch process and looped throug

Answer 1

The 2 approaches suggested above both have problems: Either writing lengthy and repetitive code that handles paging explicitly in a loop, or using Boto paginators with low-level sessions, and foregoing the advantages of higher-level Boto objects.

A solution using Python functional code to provide a high-level abstraction allows higher-level Boto methods to be used, while hiding the complexity of AWS paging:

import itertools
import typing

def iterate_result_pages(function_returning_response: typing.Callable, *args, **kwargs) -> typing.Generator:
    """A wrapper for functions using AWS paging, that returns a generator which yields a sequence of items for
    every response

    Args:
        function_returning_response: A function (or callable), that returns an AWS response with 'Items' and optionally 'LastEvaluatedKey'
        This could be a bound method of an object.

    Returns:
        A generator which yields the 'Items' field of the result for every response
    """
    response = function_returning_response(*args, **kwargs)
    yield response["Items"]
    while "LastEvaluatedKey" in response:
        kwargs["ExclusiveStartKey"] = response["LastEvaluatedKey"]
        response = function_returning_response(*args, **kwargs)
        yield response["Items"]

    return

def iterate_paged_results(function_returning_response: typing.Callable, *args, **kwargs) -> typing.Iterator:
    """A wrapper for functions using AWS paging, that returns an iterator of all the items in the responses.
    Items are yielded to the caller as soon as they are received.

    Args:
        function_returning_response: A function (or callable), that returns an AWS response with 'Items' and optionally 'LastEvaluatedKey'
        This could be a bound method of an object.

    Returns:
        An iterator which yields one response item at a time
    """
    return itertools.chain.from_iterable(iterate_result_pages(function_returning_response, *args, **kwargs))

# Example, assuming 'table' is a Boto DynamoDB table object:
all_items = list(iterate_paged_results(ProjectionExpression = 'my_field'))