all-purpose function for dumping any python thing in a mostly-readable manner (aka dump)

dump.py

import logging

# MAGIC-NUMBER: max length is just some guess at a reasonable size, e.g. 80 cols by 500 lines
def dump(value, msg='DUMP', max_length=80 * 500, stdout=False, pick=(), skip=(),
         loglevel=logging.DEBUG):
    """
    Write as verbose of a description of the value as possible to logging.DEBUG.
    
    See http://stackoverflow.com/q/27830888/116891
    
    :param value: The item of interest.
    :type value: object
    :param msg: Prefix for the logged item (default='DUMP')
    :type msg: basestring
    :param max_length: Longest allowed string length (set to None for unlimited)
    :type max_length: int
    :param stdout: If true, print instead of logging (default=False)
    :type stdout: bool
    :param pick: If specified, dump only values for these keys of the item
        (value must be a dict or allow __dict__ access).
        The name comes from http://underscorejs.org/#pick.
    :type pick: iterable of basestring
    :param skip: If specified, exclude values for these keys of the item
        (value must be a dict or allow __dict__ access).
    :type skip: iterable of basestring
    :param loglevel: Defaults to logging.DEBUG. One of the logging constants.
    :type loglevel: int
    :return: True if message dumped
    :rtype: bool
    """
    if not logging.getLogger().isEnabledFor(loglevel) and not stdout:
        return

    if pick:
        d = value if isinstance(value, dict) else value.__dict__
        filtered = {
            property_name: d[property_name]
            for property_name in pick
            if property_name in d
        }
        value = filtered

    if skip:
        d = value if isinstance(value, dict) else value.__dict__
        filtered = {
            property_name: d[property_name]
            for property_name in d
            if property_name not in skip
        }
        value = filtered

    kwargs = dict(indent=2, sort_keys=True)
    try:
        import json
        info = json.dumps(value, **kwargs)
    except Exception:
        # JSON doesn't like circular references :/
        try:
            string_repr = repr(value)
            # Replace python primitives, single-quotes, unicode, etc
            string_repr = string_repr\
                .replace('None', 'null')\
                .replace('True', 'true')\
                .replace('False', 'false')\
                .replace("u'", "'")\
                .replace("'", '"')

            # Replace object and function repr's like <MyObject ...>
            string_repr = re.sub(r':(\s+)(<[^>]+>)', r':\1"\2"', string_repr)

            # Replace tuples with lists, very naively
            string_repr = string_repr.replace('(', '[').replace(')', ']')

            info = json.dumps(json.loads(string_repr), **kwargs)
        except Exception:
            from pprint import pformat
            info = pformat(value, indent=2)

    def _out(formatted_string, *format_args):
        """Format the string and output it to the correct location."""
        if stdout:
            print(formatted_string % format_args)
        else:
            logging.log(loglevel, formatted_string, *format_args)

    if max_length is None or len(info) <= max_length:
        _out('%s: %s', msg, info)
        return True
    else:
        _out(
            'Did not dump "%s" due to length restriction. Increase max_length if desired.', msg
        )
    return False

This was created as an answer to my question/request: Work around python's json module not liking circular references - Stack Overflow