Custom "None" value when search fails

[fjsj]

Hi, thanks for this awesome lib!
One question: it seems to be impossible to set a custom return in case the search fails.

E.g.

not_found = object()
jmespath.search('foo.aaa', {'foo': {'bar': 'baz'}})  # I need `not_found`, not `None`

Is this by design or are you open to supporting that?
I see this was discussed at #113
But the proposed solution of contains isn't great, as it requires 2 searches.

[yashpokar]

You may try

jmespath.search('foo.aaa', {'foo': {'bar': 'baz'}})  or 'not_found'

[fjsj]

@yashpokar
Not enough for this problem.
This will make 'not_found' be returned when 'foo.aaa' is None, like here: {'foo': {'aaa': None}}. That's why it's important to differentiate a valid None from a not found value.

[yashpokar]

@fjsj you're right 👍

[ges0909]

Hi, thanks for this awesome lib!
One question: it seems to be impossible to set a custom return in case the search fails.

E.g.

not_found = object()
jmespath.search('foo.aaa', {'foo': {'bar': 'baz'}})  # I need `not_found`, not `None`

Is this by design or are you open to supporting that?
I see this was discussed at #113
But the proposed solution of contains isn't great, as it requires 2 searches.

Good proposal!!

It has to be differentiated between the legal value 'null' for an existing key and a non-existing key. JMESPath search should return another object than None if a key is not found.

E.g. allow to define an object NotFound as option. If not defined use None for not found. So you are backward compatible.

[cdogaru-hrp-ctr]

any updates on this?

[OndraSlama]

Any updates? This seems like quite an important thing to solve imo.

[agargenta]

+1

[theobjectivedad]

+1

[theobjectivedad]

If anyone is looking for a hack, this is what I am using until this issues is resolved. The key_exists function below will check for true existence of key:

def key_exists(key: str, obj: Any, separator='.') -> bool:

    keys = key.split(separator)
    for k in keys:
        if isinstance(obj, dict):
            if k in obj:
                obj = obj[k]
            else:
                return False
        else:
            return False
    return True

To use, check if the search result is None and if the key doesn't exist before implementing handling logic:

result = jmespath.search(search_string, source)

if result is None and not key_exists(search_string, source, separator="."):       
  if match_required:
    # Handle search_string doesn't exist but match is required...

  # Handle search_string doesn't exist and match isn't required, go ahead and assign a default value

# Implied else, search_string was found in source and it may be None

Please use caution, this will easily break when a more sophisticated jmespath expression is used.

[cdogaru-hrp-ctr]

Since jmespath doesn't care about fixing this, we've ended up using jsonpath-ng which supports everything that jmespath supports + handling None values. Best workaround.