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Python 2 is no longer supported by the community. We recommend that you migrate Python 2 apps to Python 3.

The FieldExpression Class

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Class FieldExpression allows you to compute customized content snippets for each result returned by a search.

Caution: **This solution is no longer recommended:** Apps that use this API can only run in the Python 2 runtime and will need to upgrade to a [recommended solution](/appengine/docs/legacy/standard/python/migrate-to-python3/migrating-services#migration_paths_for_bundled_services) before migrating to the Python 3 runtime.

FieldExpression is defined in the module


The constructor for class FieldExpression is defined as follows:

class FieldExpression(name, expression)

Construct an instance of class FieldExpression.

For example,

                expression='snippet("very important", content)')

constructs a field expression that returns a computed field named content-snippet with each search result, containing HTML snippets of the content field that match the query "very important".



Name of computed field.


Expression to evaluate and return.

Result value

A new instance of class FieldExpression.



A parameter has an invalid type, or an unknown attribute was passed.


A parameter has an invalid value.


An instance of class FieldExpression has the following properties:


Name of computed field.


String containing expression to evaluate and return.