There is a JSON like this:
{
"P1": "ss",
"Id": 1234,
"P2": {
"P1": "cccc"
},
"P3": [
{
"P1": "aaa"
}
]
}
How can I find all P1's value without it iterating all JSON?
P.S.: P1 can be anywhere in the JSON.
If no method can do this, can you tell me how to iterate through the JSON?
martineau
115k25 gold badges160 silver badges284 bronze badges
asked Dec 27, 2012 at 3:15
3
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']
answered Dec 27, 2012 at 18:46
martineaumartineau
115k25 gold badges160 silver badges284 bronze badges
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!
answered Dec 27, 2012 at 3:53
1
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']
martineau
115k25 gold badges160 silver badges284 bronze badges
answered Dec 27, 2012 at 6:08
AbhijitAbhijit
60k18 gold badges126 silver badges197 bronze badges
6
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]
answered Dec 27, 2012 at 3:47
jdotjdotjdotjdot
15.5k12 gold badges63 silver badges115 bronze badges
Converting the JSON to Python and recursively searching is by far the easiest:
def findall[v, k]:
if type[v] == type[{}]:
for k1 in v:
if k1 == k:
print v[k1]
findall[v[k1], k]
findall[json.loads[a], 'P1']
[where a is the string]
The example code ignores arrays. Adding that is left as an exercise.
answered Dec 27, 2012 at 3:25
Michael LortonMichael Lorton
41.7k26 gold badges95 silver badges137 bronze badges
1
Bearing in mind that json is simply a string, using regular expressions with look-ahead and look-behind can accomplish this task very quickly.
Typically, the json would have been extracted from a request to external api, so code to show how that would work has been included but commented out.
import re
#import requests
#import json
#r1 = requests.get[ ... url to some api ...]
#JSON = str[json.loads[r1.text]]
JSON = """
{
"P1": "ss",
"Id": 1234,
"P2": {
"P1": "cccc"
},
"P3": [
{
"P1": "aaa"
}
]
}
"""
rex1 = re.compile['[?' + searchkey if parentkeyname != None else searchkey
found.append[{pathkey: jsondata[searchkey]}]
else:
for key, value in jsondata.items[]:
val = Tools.search_into_json_myversion[value, searchkey, parentkeyname=key]
if len[val] != 0:
found = found + val
return found
answered Jul 28 at 14:27