Working on python json module doesn't like circular references
Other than using an external library (like jsonpickle , although I haven't tried it), is there a way to get python json
to a dump
dictionary (or list, etc.) that has circular references (just by dropping the link, that is)?
I want to use json for easier viewing of debug output.
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1 answer
Well, avoiding anything other than standard modules, here's one solution using repr
to handle circular references. EDIT: For the latest information see generic function to dump any python thing in a mostly readable way (aka dump)
# MAGIC-NUMBER: max length is just some guess at a reasonable size, e.g. 80 cols by 100 lines
def dump(value, msg='DUMP', max_length=80 * 100, stdout=False, pick=None):
"""
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
:return: True if message dumped
:rtype: bool
"""
if not logging.getLogger().isEnabledFor(logging.DEBUG) 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
kwargs = dict(indent=2, sort_keys=True)
try:
import json
info = json.dumps(value, **kwargs)
except:
# 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 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:
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.debug(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
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