A method for recursively calculating the size of a Python dict in memory.

size_estimator.py

import sys

def calculate_document_size_in_memory(doc):
    """A "size in memory" estimator for JSON documents/dicts.

    :param doc: The document or list of documents to find size of.
    :type doc: dict or list
    :return: The size of the input document(s) in bytes.
    :rtype: int

    """
    size = 0

    if isinstance(doc, (list, tuple)):
        # Add the base size the list or tuple.
        size += sys.getsizeof(type(doc)())
        # Iterate over all elements and sum their sizes.
        size += int(sum([calculate_document_size_in_memory(d) for d in doc]))
    elif isinstance(doc, dict):
        # Add the base size of a dict.
        size += sys.getsizeof(type(doc)())
        for k in doc:
            # Add size of key.
            size += calculate_document_size_in_memory(k)
            # Add size of value of key.
            size += calculate_document_size_in_memory(doc[k])
    elif isinstance(doc, (float, int, long, basestring)):
        # Base type which can be evaluated with sys.getsizeof.
        size += sys.getsizeof(doc)
    elif doc is None:
        pass
    else:
        raise ValueError("Unsizable object: {0}".format(type(doc)))

    return size