Scramjet in Python

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Scramjet is a simple reactive stream programming framework. The code is written by chaining functions that transform the streamed data, including well known map, filter and reduce.

The main advantage of Scramjet is running asynchronous operations on your data streams concurrently. It allows you to perform the transformations both synchronously and asynchronously by using the same API - so now you can "map" your stream from whatever source and call any number of API's consecutively.

Originally written on top of node.js object streams, Scramjet is now being ported into Python. This is what is happening in this repository.

Tested with Python 3.8.10 and Ubuntu 20.04.

Getting started 👷

Basic building block of Scramjet is the Stream class. It reads input in chunks, performs operations on these chunks and produces an iterable output that can be collected and written somewhere.

Creating a stream is done using read_from class method. It accepts any iterable or an object implementing .read() method as the input, and returns a Stream instance.

Transforming a stream:

• map - transform each chunk in a stream using specified function.
• filter - keep only chunks for which specified function evaluates to True.
• flatmap - run specified function on each chunk, and return all of its results as separate chunks.
• batch - convert a stream of chunks into a stream of lists of chunks.

Each of these methods return the modified stream, so they can be chained like this: some_stream.map(...).filter(...).batch(...)

Collecting data from the stream (asynchronous):

• write_to - write all resulting stream chunks into a target.
• to_list - return a list with all stream chunks.
• reduce - combine all chunks using specified function.

Examples 📚

Let's say we have a fruits.csv file like this:

orange,sweet,1
lemon,sour,2
pigface,salty,5
banana,sweet,3
cranberries,bitter,6

and we want to write the names of the sweet fruits to a separate file. To do this, write an async function like this:

with open("misc/fruits.csv") as file_in, open("sweet.txt", "w") as file_out:
    await (
        Stream
        .read_from(file_in)
        .map(lambda line: line.split(','))
        .filter(lambda record: record[1] == "sweet")
        .map(lambda record: f"{record[0]}\n")
        .write_to(file_out)
    )

and that's it!

You can find more examples in hello_datastream.py file. They don't require any additional dependencies, just the standard library, so you can run them simply with:

python hello_datastream.py

Running tests 📈

Create and activate a virtualenv:

sudo apt install python3-virtualenv
virtualenv -p python3 venv
. venv/bin/activate

Check Python version:

$ python --version
Python 3.8.10

Install dependencies:

pip install -r dev-requirements.txt

Run test cases (with activated virtualenv):

pytest

💡 HINT: add a filename if you want to limit which tests are run

If you want to enable detailed debug logging, set one of the following env variables:

PYFCA_DEBUG=1       # debug pyfca
DATASTREAM_DEBUG=1  # debug datastream
SCRAMJET_DEBUG=1    # debug both