paipa 0.2.0

Installation

pip install paipa

Overview

What it does:

• process stuff one step at a time

• allows class based and function based steps

• can scale steps independent of each other (manually)

• don’t ever do deadlocks

• never expose the developer to the concept of a thread (if she doesn’t like to)

• run in finite batches where all threads are terminated at the end

• run in continuous mode while being fed through a queue

• automatically rate limit each step to minimize memory usage

• terminate the pipeline in case of an Exception and propagate the error to the developer

What it explicitly doesn’t do (if it doesn’t, it’s not a bug!):

• pipelines with multiple different parents. Multiple parents of the same type are handled automatically though.

• auto-scale threads

• bake bread

What it shouldn’t do (if it does, it’s a bug!):

• confuse the user/developer

• hang on termination

• hog resources

Features

The lib allows for threaded pipelines as well as so-called co-routine pipelines. The main use-case is limiting peak memory usage when doing complex operations on large-ish data-sets.

>>> pipeline = paipa.Pipeline(
...     (DownloadImage, 4),
...     (StoreDatabase, 1),
... )
>>> pipeline.run()

This example will create 5 threads, 4 for downloading images, one for storing stuff to the database. The ouputs of all DownloadImage steps will be forwared to the one StoreDatabase thread via a Queue.

Thread startup and tear-down is handled by the library and doesn’t concern the programmer at all. All (known) failure cases lead to either a re-spawning of the failed thread or a controlled shutdown of the system. In no case the system should block and do nothing, if it does then it’s definitely a bug and needs to be reported.

Pipeline ingestion can be done via a separate thread or by consuming an iterable. In the case of using an iterable, an ingestion thread is created which consumes the iterable in a controled manner.

The whole pipeline can also be run in the background like this:

>>> pl = pipeline.run_forever(background=True)
>>> # do some other stuff
>>> pl.stop()  # this waits for the system to complete and do a shutdown

Co-Routine Pipelines

>>> def remove_odd(iterable):
...     for entry in iterable:
...         if entry % 2 == 0:
...             yield entry
>>> steps = [remove_odd] # Arbitrary many steps supported
>>> gen = combine_pipeline(range(100), steps)
>>> print(sum(gen))
2450

This will create nested generators which do the relevant processing. The individual steps only need to support the iterator protocol and don’t necessarily need to be generators. Memory usage may make using generators appealing though.