iterable-subprocess 0.0.9

Communicate with a subprocess using iterables: for when data is too big to fit in memory and has to be streamed

iterable-subprocess

Python context manager to communicate with a subprocess using iterables: for when data is too big to fit in memory and has to be streamed.

Data is sent to a subprocess's standard input via an iterable, and extracted from its standard output via another iterable. This allows an external subprocess to be naturally placed in a chain of iterables for streaming processing.

Installation

pip install iterable-subprocess

Usage

A single context manager iterable_subprocess is exposed. The first parameter is the args argument passed to the Popen Constructor, and the second is an iterable whose items must be bytes instances and are sent to the subprocess's standard input.

Returned from the function is an iterable whose items are bytes instances of the process's standard output.

from iterable_subprocess import iterable_subprocess

# In a real case could be a generator function that reads from the filesystem or the network
iterable_of_bytes = (
    b'first\n',
    b'second\n'
    b'third\n'
)

with iterable_subprocess(['cat'], iterable_of_bytes) as output:
    for chunk in output:
        print(chunk)

If the process exits with a non-zero error code, a SubprocessError exception will be raised, with the contents of the processes's standard error as the message. At the time of writing if the process outputs a lot to its standard error, there may be deadlock.

Usage: unzip the first file of a ZIP archive while downloading

It's possible to download the bytes of a ZIP file in Python, and unzip by passing the bytes to funzip, as in the following example.

import httpx
from iterable_subprocess import iterable_subprocess

with \
        httpx.stream('GET', 'https://www.example.com/my.zip') as r, \
        iterable_subprocess(['funzip'], r.iter_bytes()) as unzipped_chunks:

    for chunk in unzipped_chunks:
        print(chunk)

Note that it's also possible to stream unzip files without resorting to another process using stream-unzip.