GAE Search API: custom snippet length

Question

I can't seem to get a custom snippet length:

snippet = 'snippet("%s", content, 50)' % search_query
index = search.Index(name='index', namespace='namespace')
start_time = time.time()
results = index.search(
    query=Query(
        query_string=search_query,
        options=QueryOptions(
            limit=10,
            cursor=Cursor(),
            sort_options=SortOptions(
                match_scorer=search.RescoringMatchScorer()),
            returned_expressions=FieldExpression('content_snippet', snippet))))

I want a snippet which is 50 characters long, instead of the default 160 characters. According to this documentation, the snippet function can get 3 arguments: the search term, the field to snippet over and an optional snippet length.

It seems as if it's completely ignoring the third parameter I pass... Am I doing something wrong?

Answer 1

It seems that snippets don't work on the devserver. See the documentation: https://developers.google.com/appengine/docs/python/search/devserver

Using the Python Development Server

The Python development server runs on your local machine and emulates most of the Search API's capabilities. However, a few features are not currently available on the server. For the moment, you should not attempt to use the following features when you run on the development server:

Functions in expressions

These functions are not available:

• snippet()
• geopoint()
• distance()
• pow()

As advoretsky said, returned_expressions needs to be an iterable. From the docs:

returned_expressions

An iterable of FieldExpression to evaluate and return in search results.

Further, be sure you import the right Query and QueryOptions, both are also found in google.appengine.ext.ndb. I prefer to import them so they have a prefix, things are better readable then ;-)

from google.appengine.ext import ndb
from google.appengine.api import search

# Notice the nice distinction
ndb.Query
search.Query

Answer 2

I didn't try it for myself yet, but according to the reference returned_expressions should be iterable. See also an example on Query and Sorting Options and change to

returned_expressions=[FieldExpression('content_snippet', snippet)]