[BEAM-8140] Python API: PTransform should be immutable and reusable

• Type: Bug
• Status: Open
• Priority: P3
• Resolution: Unresolved
• Component/s: sdk-py-core
• Assignee: Unassigned
• Reporter: Chris Suchanek
• Created: 03/Sep/19 23:03
• Updated: 04/Jun/22 12:40

Description

While the Java API seems fine the Python API is (at least) counterintuitive.

Let's see the following example:

p1 = beam.Pipeline()
p2 = beam.Pipeline()
node = 'ReadTrainData' >> beam.io.ReadFromText("/tmp/aaa.txt")
p1 | node 
p2 | node //fails here 

The code above will fail because the node somehow remembers that it was already attached to p1. In fact, unlike in Java, the | (apply) method is defined on the PTransform.

If any, only the pipeline object should be mutable here.