In Python, using jsonpath-rw to get values for specific attribute (json/dict)

Question

Here's my json:

{
   'test': [
        { "id": "1", "description": "Test 1" },
        { "id": "2", "description": "Test 2" }
    ]
}

I'm trying to get the value for id where description is "Test 1".

I found the following example on the JsonPath page:

$..book[?(@.price<10)]

When trying to parse the following jsonxpath expression:

parse('$..test[?(@.description="Test 1")].id')

I get the following error:

jsonpath_rw.lexer.JsonPathLexerError: Error on line 1, col 7: Unexpected character: ?

What am I doing wrong? Alternatively, is there a better way to do this?

Oddly enough, looking at the lexer code, jsonpath-rw doesn't appear to support the ?(boolean) filter mechanism at all. — voithos
– voithos, Commented May 24, 2015 at 1:13

voithos · Accepted Answer · 2015-05-24 01:40:22Z

10

It appears that jsonpath-rw doesn't support this feature. Perhaps consider another library? ObjectPath looks promising:

>>> import objectpath
>>> json_obj = { ... } # This has to be pre-parsed
>>> tree = objectpath.Tree(json_obj)
>>> ids = tree.execute('$..test[@.description is "Test 1"].id')
>>> print list(ids)
["1"]

It doesn't quite follow the JsonPath syntax exactly, but it's quite similar, at least from a perfunctory survey. Documentation is also available.

Of course, if your JSON will always be in the same form (i.e. you won't have to deal with missing child objects, etc), then you could easily do the same query using a list comprehension, or something similar.

json = { ... }
ids = [t['id'] for t in json['test'] if t['description'] == 'Test 1']

answered May 24, 2015 at 1:40

voithos

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1 Comment

Adrian Kalbarczyk Over a year ago

Just keep in mind that .. operator (recursive descent/deep search) is very slow. Use . if you are sure that test is in the root of the document and only in the root of the document.

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