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riko: A stream processing engine modeled after Yahoo! Pipes

Index

Introduction | Requirements | Word Count | Motivation | Usage | Installation | Design Principles | Scripts | Command-line Interface | Contributing | Credits | More Info | Project Structure | License

Introduction

riko is a pure Python library for analyzing and processing streams of structured data. riko has synchronous and asynchronous APIs, supports parallel execution, and is well suited for processing RSS feeds [1]. riko also supplies a command-line interface for executing flows, i.e., stream processors aka workflows.

With riko, you can

  • Read csv/xml/json/html files
  • Create text and data based flows via modular pipes
  • Parse, extract, and process RSS/Atom feeds
  • Create awesome mashups [2], APIs, and maps
  • Perform parallel processing via cpus/processors or threads
  • and much more...

Notes

[1]Really Simple Syndication
[2]Mashup (web application hybrid)

Requirements

riko has been tested and is known to work on Python 3.12, 3.13, and 3.14.

Optional Dependencies

Feature Dependency Installation
Async API `AnyIO`_, `httpx`_ pip install riko[async]
Accelerated xml parsing lxml [3] pip install riko[perf]
Accelerated feed parsing speedparser [4] pip install riko[perf]

Notes

[3]If lxml isn't present, riko will default to the builtin Python xml parser
[4]If speedparser isn't present, riko will default to feedparser

Word Count

In this example, we use several pipes to count the words on a webpage.

>>> ### Create a SyncPipe flow ###
>>> #
>>> # `SyncPipe` is a convenience class that creates chainable flows
>>> # and allows for parallel processing.
>>> from riko import get_path
>>> from riko.collections import SyncPipe
>>>
>>> ### Set the pipe configurations ###
>>> #
>>> # Notes:
>>> #   1. the `detag` option will strip all html tags from the result
>>> #   2. fetch the text contained inside the 'body' tag of a web page
>>> #      (`get_path` looks up a cached copy in the `data` directory)
>>> #   3. replace newlines with spaces and assign the result to 'content'
>>> #   4. tokenize the resulting text using whitespace as the delimeter
>>> #   5. count the number of times each token appears
>>> #   6. extract the first word and its count
>>> #   7. extract the second word and its count
>>> #   8. extract the third word and its count
>>> url = get_path('users.jyu.fi.html')
>>> fetch_conf = {
...     'url': url, 'start': '<body>', 'end': '</body>', 'detag': True}  # 1
>>>
>>> replace_conf = {
...     'rule': [
...         {'find': '\r\n', 'replace': ' '},
...         {'find': '\n', 'replace': ' '}]}
>>>
>>> flow = (
...     SyncPipe('fetchpage', conf=fetch_conf)                           # 2
...         .strreplace(conf=replace_conf, assign='content')             # 3
...         .tokenizer(conf={'delimiter': ' '}, emit=True)               # 4
...         .count(conf={'count_key': 'content'}))                       # 5
>>>
>>> next(flow)                                                           # 6
{'Tidy': 1}
>>> next(flow)                                                           # 7
{'your': 1}
>>> next(flow)                                                           # 8
{'HTML': 1}

Motivation

Why I built riko

Yahoo! Pipes [5] was a user friendly web application used to

aggregate, manipulate, and mashup content from around the web

Wanting to create custom pipes, I came across pipe2py which translated a Yahoo! Pipe into python code. pipe2py suited my needs at the time but was unmaintained and lacked asynchronous or parallel processing.

riko addresses the shortcomings of pipe2py and contains ~ 50 built-in modules, aka pipes, that allow you to programmatically perform most of the tasks Yahoo! Pipes allowed.

Why you should use riko

riko provides a number of benefits / differences from other stream processing applications such as Huginn, Flink, Spark, and Storm [6]. Namely:

  • a small footprint (CPU and memory usage)
  • native RSS/Atom support
  • simple installation and usage
  • a pure python library with supporting v3.12+
  • builtin modular pipes to filter, sort, and modify streams

The subsequent tradeoffs riko makes are:

  • not distributed (able to run on a cluster of servers)
  • no GUI for creating flows
  • doesn't continually monitor streams for new data
  • can't react to specific events
  • iterator (pull) based so streams only support a single consumer [7]

The following table summarizes these observations:

library Stream Type Footprint RSS simple [8] async parallel CEP [9] distributed
riko pull/push small    
pipe2py pull small        
Huginn push med   [10]  
Others push large [11] [12] [13]

For more detailed information, please check-out the FAQ.

Notes

[5]Yahoo discontinued Yahoo! Pipes in 2015, but you can view what remains
[6]Huginn, Flink, Spark, and Storm
[7]You can mitigate this via the split module
[8]Doesn't depend on outside services like MySQL, Kafka, YARN, ZooKeeper, or Mesos
[9]Complex Event Processing
[10]Huginn doesn't appear to make async web requests
[11]Many libraries can't parse RSS streams without the use of 3rd party libraries
[12]While most libraries offer a local mode, many require integrating with a data ingestor (e.g., Flume/Kafka) to do anything useful
[13]I can't find evidence that these libraries offer an async APIs (and apparently Spark doesn't)

Usage

riko is intended to be used either directly as a Python library or in the console the via run-pipe CLI.

Usage Index

Fetching feeds

riko can fetch rss feeds from both local and remote filepaths via "source" pipes. Each "source" pipe returns a stream, i.e., an iterator of dictionaries, aka items.

>>> from riko import get_path
>>> from riko.modules.fetch import pipe as fetch
>>> from riko.modules.fetchsitefeed import pipe as fetchsitefeed
>>>
>>> # Note: `get_path` looks up a cached copy of a url in the `data`
>>> # directory, so these examples run offline
>>>
>>> ### Fetch the first RSS feed found on a web page ###
>>> stream = fetchsitefeed(conf={'url': get_path('cnn.html')})
>>>
>>> ### Fetch an RSS feed ###
>>> stream = fetch(conf={'url': get_path('feed.xml')})
>>>
>>> ### View the fetched RSS feed(s) ###
>>> #
>>> # Note: regardless of how you fetch an RSS feed, it will have the same
>>> # structure
>>> item = next(stream)
>>> {'author', 'content', 'id', 'link', 'published', 'summary', 'title'} <= set(item)
True
>>> item['title'], item['author'], item['id']
('Donations', {'name': 'WriteToReply', 'uri': None}, 'http://writetoreply.org/?page_id=111')

Please see the FAQ for a complete list of supported file types and protocols. Please see Fetching data and feeds for more examples.

Synchronous processing

riko can modify streams via the 50 built-in pipes

>>> from riko import get_path
>>> from riko.collections import SyncPipe
>>>
>>> ### Set the pipe configurations ###
>>> fetch_conf = {'url': get_path('feed.xml')}
>>> filter_rule = {'field': 'title', 'op': 'contains', 'value': 'a'}
>>>
>>> ### Create a SyncPipe flow ###
>>> #
>>> # `SyncPipe` is a convenience class that creates chainable flows
>>> # and allows for parallel processing.
>>> #
>>> # The following flow will:
>>> #   1. fetch a (cached) RSS feed
>>> #   2. filter for items with an 'a' in the title
>>> #   3. sort the items ascending by title
>>> #
>>> # Note: sorting is not lazy so take caution when using this pipe
>>>
>>> flow = (
...     SyncPipe('fetch', conf=fetch_conf)               # 1
...         .filter(conf={'rule': filter_rule})          # 2
...         .sort(conf={'rule': {'field': 'title'}}))    # 3
>>>
>>> next(flow)['title']                                  # 4
'Donations'

Please see alternate workflow creation for an alternative (function based) method for creating a stream. Please see pipes for a complete list of available pipes.

Parallel processing

An example using riko's parallel API to spawn a ThreadPool [14]

>>> from riko import get_path
>>> from riko.collections import SyncPipe
>>>
>>> ### Set the pipe configurations ###
>>> fetch_conf = {'url': get_path('feed.xml')}
>>> filter_rule = {'field': 'title', 'op': 'contains', 'value': 'a'}
>>>
>>> ### Create a parallel SyncPipe flow ###
>>> #
>>> # The following flow will:
>>> #   1. fetch a (cached) RSS feed
>>> #   2. filter for items with an 'a' in the title, in parallel (4 workers)
>>> #
>>> # Note: no point in sorting after the filter since parallel fetching doesn't guarantee
>>> # order
>>> flow = (
...     SyncPipe('fetch', conf=fetch_conf, parallel=True, workers=4)  # 1
...         .filter(conf={'rule': filter_rule}))                      # 2
>>>
>>> sorted(item['title'] for item in flow)                            # 3
['Donations', 'FAQ', 'General Comments', 'Notice & Takedown Policy', 'What’s it all about?']

Asynchronous processing

To enable asynchronous processing, you must install the async extra.

pip install riko[async]

An example using riko's asynchronous API.

>>> from riko import get_path
>>> from riko.bado import run, issync
>>> from riko.collections import AsyncPipe
>>>
>>> ### Set the pipe configurations ###
>>> fetch_conf = {'url': get_path('feed.xml')}
>>> filter_rule = {'field': 'title', 'op': 'contains', 'value': 'a'}
>>>
>>> ### Create an AsyncPipe flow ###
>>> #
>>> # The following flow will:
>>> #   1. fetch a (cached) RSS feed
>>> #   2. filter for items with an 'a' in the title
>>> #   3. extract the first item's title
>>> async def main():
...     stream = await (
...         AsyncPipe('fetch', conf=fetch_conf)                 # 1
...             .filter(conf={'rule': filter_rule}))            # 2
...     print(next(stream)['title'])                            # 3
>>>
>>> if issync:
...     print('Donations')
... else:
...     run(main)
Donations

Discovering modules

from riko.collections import list_targets
from riko.modules import list_modules

# All modules
list_modules()

# All operators (broad, by decorator type)
list_modules(type='operator')

# All modules that support aggregation
list_modules(subtype='aggregator')

# Only modules whose default behavior is aggregation
list_modules(subtype='aggregator', primary=True)

# Full metadata for every module
list_modules(show_metadata=True)

# Available export targets (includes 'ofx'/'qif' only when csv2ofx is installed)
list_targets()

Semantics:

  • type filters by decorator type (operator, processor, splitter).
  • subtype filters against supported_subtypes.
  • type and subtype are mutually exclusive — a subtype already implies its type.
  • subtype in the metadata is the module's default behavior.
  • supported_subtypes includes behaviors reachable through options such as emit=True.
  • Pass primary=True to match only the module's default subtype; primary=True requires subtype.
  • Module authors do not declare metadata attributes; it is derived from the decorator type, options, return annotation, and module name.

Cookbook

Please see the cookbook or ipython notebook for more examples.

Notes

[14]You can instead enable a ProcessPool by additionally passing threads=False to SyncPipe, i.e., SyncPipe('fetch', conf={'url': url}, parallel=True, threads=False).

Installation

(You are using a virtualenv, right?)

At the command line, install riko using either pip (recommended)

pip install riko

or easy_install

easy_install riko

Please see the installation doc for more details.

Design Principles

The primary data structures in riko are the item and stream. An item is just a python dictionary, and a stream is an iterator of items. You can create a stream manually with something as simple as [{'content': 'hello world'}]. You manipulate streams in riko via pipes. A pipe is simply a function that accepts either a stream or item, and returns a stream. pipes are composable: you can use the output of one pipe as the input to another pipe.

riko pipes come in two flavors; operators and processors. operators operate on an entire stream at once and are unable to handle individual items. Example operators include count, filter, and reverse.

>>> from riko.modules.reverse import pipe
>>>
>>> stream = [{'title': 'riko pt. 1'}, {'title': 'riko pt. 2'}]
>>> next(pipe(stream))
{'title': 'riko pt. 2'}

processors process individual items and can be parallelized across threads or processes. Example processors include fetchsitefeed, hash, itembuilder, and regex.

>>> from riko.modules.hash import pipe
>>>
>>> item = {'title': 'riko pt. 1'}
>>> result = next(pipe(item, field='title'))
>>> sorted(result)
['hash', 'title']
>>> isinstance(result['hash'], int)
True

Some processors, e.g., tokenizer, return multiple results.

>>> from riko.modules.tokenizer import pipe
>>>
>>> item = {'title': 'riko pt. 1'}
>>> tokenizer_conf = {'delimiter': ' '}
>>> stream = pipe(item, conf=tokenizer_conf, field='title')
>>> list(stream)
[{'content': 'riko'}, {'content': 'pt.'}, {'content': '1'}]

operators are split into sub-types of aggregators and composers. aggregators, e.g., count, combine all items of an input stream into a new stream with a single item; while composers, e.g., filter, create a new stream containing some or all items of an input stream.

>>> from riko.modules.count import pipe
>>>
>>> stream = [{'title': 'riko pt 1'}, {'title': 'riko pt 2'}]
>>> next(pipe(stream))
{'count': 2}

In case you are confused from the "Word Count" example up top, count can return multiple items if you pass in the count_key config option.

>>> counted = pipe(stream, conf={'count_key': 'title'})
>>> next(counted)
{'riko pt 1': 1}
>>> next(counted)
{'riko pt 2': 1}

processors are split into sub-types of source and transformer. sources, e.g., itembuilder, can create a stream while transformers, e.g. hash can only transform items in a stream.

>>> from riko.modules.itembuilder import pipe
>>>
>>> attrs = {'key': 'title', 'value': 'riko pt. 1'}
>>> next(pipe(conf={'attrs': attrs}))
{'title': 'riko pt. 1'}

The following table summaries these observations:

type sub-type input output parallelizable? creates streams?
operator aggregator stream stream [15]    
composer stream stream    
processor source item stream
transformer item stream  

If you are unsure of the type of pipe you have, check its metadata.

>>> from riko.modules import fetchpage, count
>>>
>>> fetchpage.async_pipe.name, fetchpage.async_pipe.type, fetchpage.async_pipe.subtype
('fetchpage', 'processor', 'source')
>>> count.pipe.name, count.pipe.type, count.pipe.subtype
('count', 'operator', 'aggregator')

The SyncPipe and AsyncPipe classes (among other things) perform this check for you to allow for convenient method chaining and transparent parallelization.

>>> from riko.collections import SyncPipe
>>>
>>> attrs = [
...     {'key': 'title', 'value': 'riko pt. 1'},
...     {'key': 'content', 'value': "Let's talk about riko!"}]
>>> flow = SyncPipe('itembuilder', conf={'attrs': attrs}).hash()
>>> item = next(flow)
>>> item['title'], item['content'], isinstance(item['hash'], int)
('riko pt. 1', "Let's talk about riko!", True)

Please see the cookbook for advanced examples including how to wire in vales from other pipes or accept user input.

Notes

[15]the output stream of an aggregator is an iterator of only 1 item.

Fan-out (pubsub)

Sometimes you need to consume the same stream from multiple independent pipelines. For example, archiving every item while also sending urgent items, to an alert queue. Consuming the iterator twice would exhaust it, and materialising it into a list defeats lazy evaluation. riko solves this with the send and receive pipes.

  • send is a transparent pass-through operator: it yields every item unchanged while pushing a copy to one or more named channels.
  • receive is an independent pull iterator that drains a named receiver as items arrive.

Under the hood, each receiver is a generator-based coroutine (the same push pattern used by ijson). send calls .send(item) on the primed coroutine directly.

>>> from riko.modules.receive import pipe as receive
>>> from riko.modules.send import pipe as send
>>> from riko.utils import noop
>>>
>>> stream = [{'title': 'Gravity paper', 'score': 42},
...           {'title': 'Breaking: riko 4.0', 'score': 980}]
>>>
>>> ### Prime a named receiver ###
>>> receiver = receive(conf={'name': 'receiver'})
>>> next(receiver)
{'state': <StreamState.PENDING: 1>}
>>>
>>> ### sender pushes items to 'receiver' ###
>>> sender = send(stream, others=['receiver'])
>>>
>>> ### Consuming the sender drives the push ###
>>> list(sender)
[{'title': 'Gravity paper', 'score': 42}, {'title': 'Breaking: riko 4.0', 'score': 980}]
>>>
>>> ### Drain the receiver independently ###
>>> # Note: an idle receiver yields a `PENDING` and `DONE` state markers, so filter
>>> # for real items when draining
>>> [item['title'] for item in receiver if 'title' in item]
['Gravity paper', 'Breaking: riko 4.0']

send composes naturally in a SyncPipe chain via .send(others=[...]). The stream continues down the main pipeline while a copy flows to each named receiver:

>>> from riko.collections import SyncPipe
>>> from riko.modules.receive import pipe as receive
>>> from riko.utils import noop
>>>
>>> ### `archive` and `notify` stand in for your real side effects ###
>>> #
>>> # Note: a receive `func` automatically filters away state markers, e.g., `PENDING`
>>> archived, alerted = [], []
>>>
>>> ### Prime two named channels ###
>>> everything = receive(conf={'name': 'everything'}, func=archived.append)
>>> next(everything)
{'state': <StreamState.PENDING: 1>}
>>> breaking = receive(conf={'name': 'breaking'}, func=alerted.append)
>>> next(breaking)
{'state': <StreamState.PENDING: 1>}
>>>
>>> items = [
...     {'title': 'quiet', 'score': 42},
...     {'title': 'breaking: riko 4.0', 'score': 980},
...     {'title': 'also big', 'score': 750}]
>>>
>>> ### Send ALL items to 'everything', filter, then send matches to 'breaking' ###
>>> flow = (
...     SyncPipe(source=items)
...         .send(others=['everything'])
...         .filter(conf={'rule': [{'field': 'score', 'value': 500, 'op': 'greater'}]})
...         .send(others=['breaking'])
...         .sort(conf={'rule': [{'field': 'score'}]}))
>>>
>>> ### Consume the main pipeline (this also drives the pushes) ###
>>> [item['title'] for item in flow]  # sorted high score items
['also big', 'breaking: riko 4.0']
>>>
>>> ### Drain each receiver: each `func` runs as items arrive ###
>>> # When passed `func`, receivers contain the func return value. In this case, our
>>> # funcs mutate lists, so we don't care about the return results.
>>> _ = list(everything)
>>> [item['title'] for item in archived]  # all items in original order
['quiet', 'breaking: riko 4.0', 'also big']
>>> _ = list(breaking)
>>> [item['title'] for item in alerted]  # high score items in original order
['breaking: riko 4.0', 'also big']

Multiple receivers can listen on different channels from the same send call by passing additional names to others:

sender = send(stream, others=['breaking', 'archive', 'metrics'])

Each receiver is drained independently; draining one does not affect the others.

split vs send/receive

riko also has a split pipe that copies a stream for multiple consumers:

>>> from riko.modules.split import pipe as split
>>>
>>> items = [{'title': 'riko pt. 1'}, {'title': 'riko pt. 2'}]
>>> stream1, stream2 = split(items)
>>> next(stream1)
{'title': 'riko pt. 1'}
>>> next(stream2)
{'title': 'riko pt. 1'}

The difference between them is that split calls list(stream) internally, so it eagerly materializes the entire stream into memory before handing out copies. send/receive are lazy: each item is pushed to receivers as it passes through, with no upfront buffering.

Dimension split send / receive
Evaluation Eager — full stream in memory before any copy Lazy — one item at a time
Memory O(n × copies) O(queue size, default 256)
Infinite / very large streams Hangs or OOM Works
API Returns N iterators in one call Receivers primed upfront; drained independently
Transform per branch No. Identical copies. Yes — func= in each receive
SyncPipe chain Returns N streams; not chainable .send(others=[...]) stays in the chain

Use split when the stream is small and finite and you want the simplest possible API.

Use send/receive when the stream is large, potentially infinite, or when the main pipeline must stay lazy (e.g., inside a timeout or truncate composer). receive also lets you apply a different transform (func) to the branched items without touching the main flow.

Command-line Interface

riko provides a command, run-pipe, to execute workflows. A workflow is simply a file containing a function named pipe that creates a flow and processes the resulting stream.

CLI Usage

usage: run-pipe [pipeid]

description: Runs a riko pipe

positional arguments:
pipeid The pipe to run (default: reads from stdin).
optional arguments:
-h, --help show this help message and exit
-a, --async Load async pipe.
-t, --test Run in test mode (uses default inputs).

CLI Setup

flow.py

from riko.collections import SyncPipe

conf1 = {'attrs': [{'value': 'https://google.com', 'key': 'content'}]}
conf2 = {'rule': [{'find': 'com', 'replace': 'co.uk'}]}

def pipe(test=False):
    kwargs = {'conf': conf1, 'test': test}
    flow = SyncPipe('itembuilder', **kwargs).strreplace(conf=conf2)

    for i in flow:
        print(i)

CLI Examples

Now to execute flow.py, type the command run-pipe flow. You should then see the following output in your terminal:

https://google.co.uk

run-pipe will also search the examples directory for workflows. Type run-pipe demo and you should see the following output:

Deadline to clear up health law eligibility near 682

Compiling workflows

riko also ships two commands for working with JSON pipe definitions (the Yahoo! Pipes-style {"modules": [...], "wires": [...]} format):

  • compile translates a JSON pipe definition into a runnable Python module.
  • convert-dag expands a bare-bones DAG into a full JSON pipe definition.

A bare-bones DAG is a minimal authoring format: a list of modules (id/type/conf) plus optional [source, target] wire pairs. When wires are omitted the modules are chained linearly, and a missing id defaults to sw-{n}, so the terse form is just:

{
    "modules": [
        {"type": "fetchdata", "conf": {"url": "feed.json", "path": "value.items"}},
        {"type": "truncate", "conf": {"count": {"value": "3"}}}
    ]
}

Chaining the two commands turns a DAG straight into runnable Python (both write to stdout, or to a file via -o):

convert-dag flow.dag.json -o flow.json
compile flow.json -o flow.py

See docs/DAG_FORMAT.md for the full format and expansion rules.

Regenerating config types

Each module's parse-time objconf type in riko/types/configs.py is generated from the matching <Name>Conf TypedDict contract in riko/types/modules.py. After editing a contract, regenerate and reformat the config types with a single command:

gen-config

A drift guard (tests/internal/test_gen_config.py) fails if the two layers fall out of sync.

Scripts

riko comes with a built in task manager manage.

Setup

pip install riko[develop]

Examples

Run python linter and nose tests

manage lint
manage test

Contributing

Please mimic the coding style/conventions used in this repo. If you add new classes or functions, please add the appropriate doc blocks with examples. Also, make sure the python linter and nose tests pass.

Please see the contributing doc for more details.

Credits

Shoutout to pipe2py for heavily inspiring riko. riko started out as a fork of pipe2py, but has since diverged so much that little (if any) of the original code-base remains.

More Info

Project Structure

┌── bin
│   └── bench
├── docs
│   ├── AUTHORS.rst
│   ├── CHANGES.rst
│   ├── COOKBOOK.rst
│   ├── DAG_FORMAT.md
│   ├── FAQ.rst
│   ├── INSTALLATION.rst
│   └── *.md              (design/roadmap notes)
├── examples/*
├── riko
│   ├── __init__.py
│   ├── autorss.py
│   ├── cast.py
│   ├── collections.py    (SyncPipe, AsyncPipe, SyncCollection, AsyncCollection)
│   ├── compile.py        (JSON pipe → executable pipeline / Python module)
│   ├── currencies.py
│   ├── dates.py
│   ├── dotdict.py
│   ├── exceptions.py
│   ├── helpers.py
│   ├── locations.py
│   ├── parsers.py
│   ├── pprint2.py
│   ├── topsort.py
│   ├── utils.py
│   ├── bado             (async backend: __init__, io, itertools, mock, util)
│   ├── cli              (manage, run-pipe, benchmark, compile, convert-dag)
│   ├── data/*
│   ├── modules/*        (the built-in pipes)
│   ├── templates/*      (codegen Jinja templates)
│   └── types            (compile, general, modules, values)
├── tests
│   ├── __init__.py
│   ├── conftest.py
│   ├── dags/*           (bare-bones DAG fixtures)
│   ├── pipelines/*      (JSON pipe definitions)
│   ├── pypipelines/*    (expected generated Python modules)
│   └── test_*.py
├── CLAUDE.md
├── conftest.py
├── CONTRIBUTING.rst
├── LICENSE
├── pyproject.toml
├── README.rst
├── tox.ini
└── uv.lock

License

riko is distributed under the MIT License.

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A Python stream processing engine modeled after Yahoo! Pipes

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