streamsx.topology.schema module

Schemas for streams.

On a structured stream a tuple is a sequence of attributes, and an attribute is a named value of a specific type.

The supported types are defined by IBM Streams Streams Processing Language (SPL).

class streamsx.topology.schema.CommonSchema

Bases: enum.Enum

Common stream schemas for interoperability within Streams applications.

Streams application can publish streams that are subscribed to by other applications. Use of common schemas allow streams connections regardless of the application implementation language.

Python applications publish streams using publish() and subscribe using subscribe().

• Python - Stream constains Python objects.
• Json - Stream contains JSON objects.
• String - Stream contains strings.
• Binary - Stream contains binary tuples.
• XML - Stream contains XML documents.

Binary = <streamsx.topology.schema.StreamSchema object>

Stream where each tuple is a binary object (sequence of bytes).

Warning

Binary is not yet supported for Python applications.

Json = <streamsx.topology.schema.StreamSchema object>

Stream where each tuple is logically a JSON object.

Json can be used as a natural interchange format between Streams applications implemented in different programming languages. All languages supported by Streams support publishing and subscribing to JSON streams.

A Python callable receives each tuple as a dict as though it was created from json.loads(json_formatted_str) where json_formatted_str is the JSON formatted representation of tuple.

Python objects that are to be converted to JSON objects must be supported by JSONEncoder. If the object is not a dict then it will be converted to a JSON object with a single key payload containing the value.

Python = <streamsx.topology.schema.StreamSchema object>

Stream where each tuple is a Python object.

Python streams can only be used by Python applications.

String = <streamsx.topology.schema.StreamSchema object>

Stream where each tuple is a string.

String can be used as a natural interchange format between Streams applications implemented in different programming languages. All languages supported by Streams support publishing and subscribing to string streams.

A Python callable receives each tuple as a str object.

Python objects are converted to strings using str(obj).

XML = <streamsx.topology.schema.StreamSchema object>

Stream where each tuple is an XML document.

Warning

XML is not yet supported for Python applications.

class streamsx.topology.schema.StreamSchema(schema)

Bases: object

Defines a schema for a structured stream.

On a structured stream a tuple is a sequence of attributes, and an attribute is a named value of a specific type.

The supported types are defined by IBM Streams Streams Processing Language and include such types as int8, int16, rstring and list<float32>.

A schema is defined with the syntax tuple<type name [,...]>, for example:

tuple<rstring id, timestamp ts, float64 value>

represents a schema with three attributes suitable for a sensor reading.

A StreamSchema can be created by passing a string of the for tuple<...> or by passing the name of an SPL type from an SPL toolkit, for example com.ibm.streamsx.transportation.vehicle::VehicleLocation.

Attribute names must start with an ASCII letter or underscore, followed by ASCII letters, digits, or underscores.

Parameters:schema (str) – Schema definition. Either a schema definition or the name of an SPL type.

extend(schema)

Extend a structured schema by another.

For example extending tuple<rstring id, timestamp ts, float64 value> with tuple<float32 score> results in tuple<rstring id, timestamp ts, float64 value, float32 score>.

Parameters:schema (StreamSchema) – Schema to extend this schema by. Returns:New schema that is an extension of this schema. Return type:StreamSchema

schema()

Private method. May be removed at any time.

spl_json()

Private method. May be removed at any time.