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Async interface

An async interface is provided via the function async_stream_unzip. Its usage is exactly the same as stream_zip except that:

  1. The input must be an async iterable of bytes.
  2. The member files are output as an async iterable of tuples.
  3. The data of each member file is returned as an async iterable of bytes.
from stream_unzip import async_stream_unzip
import httpx

async def zipped_chunks(client):
    # Iterable that yields the bytes of a zip file
    async with'GET', '') as r:
        async for chunk in r.aiter_bytes(chunk_size=65536):
            yield chunk

async def main():
    async with httpx.AsyncClient() as client:
        async for file_name, file_size, unzipped_chunks in async_stream_unzip(
            async for chunk in unzipped_chunks:


Under the hood async_stream_unzip uses threads as a layer over the synchronous stream_unzip function. This has two consequences:

  1. A possible performance penalty over a theoretical implementation that is pure async without threads.

  2. The contextvars context available in the async iterables of files or data is a shallow copy of the context where async_stream_unzip is called from.

This means that existing context variables are available inside the input iterable, but any changes made to the context itself from inside the iterable will not propagate out to the original context. Changes made to mutable data structures that are part of the context, for example dictionaries, will propagate out.

This does not affect Python 3.6, because contextvars is not available.