How to find a particular json value by key?
I had the same issue just the other day. I wound up just searching through the entire object and accounted for both lists and dicts. The following snippets allows you to search for the first occurrence of a multiple keys.
import json
def deep_search(needles, haystack):
found = {}
if type(needles) != type([]):
needles = [needles]
if type(haystack) == type(dict()):
for needle in needles:
if needle in haystack.keys():
found[needle] = haystack[needle]
elif len(haystack.keys()) > 0:
for key in haystack.keys():
result = deep_search(needle, haystack[key])
if result:
for k, v in result.items():
found[k] = v
elif type(haystack) == type([]):
for node in haystack:
result = deep_search(needles, node)
if result:
for k, v in result.items():
found[k] = v
return found
deep_search(["P1", "P3"], json.loads(json_string))
It returns a dict with the keys being the keys searched for. Haystack is expected to be a Python object already, so you have to do json.loads before passing it to deep_search.
Any comments for optimization are welcomed!
My approach to this problem would be different.
As JSON doesn't allow depth first search, so convert the json to a Python Object, feed it to an XML decoder and then extract the Node you are intending to search
from xml.dom.minidom import parseString
import json
def bar(somejson, key):
def val(node):
# Searches for the next Element Node containing Value
e = node.nextSibling
while e and e.nodeType != e.ELEMENT_NODE:
e = e.nextSibling
return (e.getElementsByTagName('string')[0].firstChild.nodeValue if e
else None)
# parse the JSON as XML
foo_dom = parseString(xmlrpclib.dumps((json.loads(somejson),)))
# and then search all the name tags which are P1's
# and use the val user function to get the value
return [val(node) for node in foo_dom.getElementsByTagName('name')
if node.firstChild.nodeValue in key]
bar(foo, 'P1')
[u'cccc', u'aaa', u'ss']
bar(foo, ('P1','P2'))
[u'cccc', u'cccc', u'aaa', u'ss']
As I said in my other answer, I don't think there is a way of finding all values associated with the "P1"
key without iterating over the whole structure. However I've come up with even better way to do that which came to me while looking at @Mike Brennan's answer to another JSON-related question How to get string objects instead of Unicode from JSON?
The basic idea is to use the object_hook
parameter that json.loads()
accepts just to watch what is being decoded and check for the sought-after value.
Note: This will only work if the representation is of a JSON object
(i.e. something enclosed in curly braces {}
), as in your sample.
from __future__ import print_function
import json
def find_values(id, json_repr):
results = []
def _decode_dict(a_dict):
try:
results.append(a_dict[id])
except KeyError:
pass
return a_dict
json.loads(json_repr, object_hook=_decode_dict) # Return value ignored.
return results
json_repr = '{"P1": "ss", "Id": 1234, "P2": {"P1": "cccc"}, "P3": [{"P1": "aaa"}]}'
print(find_values('P1', json_repr))
(Python 3) output:
['cccc', 'aaa', 'ss']
Using json
to convert the json to Python objects and then going through recursively works best. This example does include going through lists.
import json
def get_all(myjson, key):
if type(myjson) == str:
myjson = json.loads(myjson)
if type(myjson) is dict:
for jsonkey in myjson:
if type(myjson[jsonkey]) in (list, dict):
get_all(myjson[jsonkey], key)
elif jsonkey == key:
print myjson[jsonkey]
elif type(myjson) is list:
for item in myjson:
if type(item) in (list, dict):
get_all(item, key)