fileio.rst

Asynchronous file I/O support

AnyIO provides asynchronous wrappers for blocking file operations. These wrappers run blocking operations in worker threads.

Example:

from anyio import open_file, run


async def main():
    async with await open_file('/some/path/somewhere') as f:
        contents = await f.read()
        print(contents)

run(main)

The wrappers also support asynchronous iteration of the file line by line, just as the standard file objects support synchronous iteration:

from anyio import open_file, run


async def main():
    async with await open_file('/some/path/somewhere') as f:
        async for line in f:
            print(line, end='')

run(main)

To wrap an existing open file object as an asynchronous file, you can use .wrap_file:

from anyio import wrap_file, run


async def main():
    with open('/some/path/somewhere') as f:
        async for line in wrap_file(f):
            print(line, end='')

run(main)

Note

Closing the wrapper also closes the underlying synchronous file object.

FileStreams

Asynchronous path operations

AnyIO provides an asynchronous version of the pathlib.Path class. It differs with the original in a number of ways:

• Operations that perform disk I/O (like ~pathlib.Path.read_bytes) are run in a worker thread and thus require an await`
• Methods like ~pathlib.Path.glob return an asynchronous iterator that yields asynchronous ~.Path objects
• Properties and methods that normally return pathlib.Path objects return ~.Path objects instead
• Methods and properties from the Python 3.10 API are available on all versions
• Use as a context manager is not supported, as it is deprecated in pathlib

For example, to create a file with binary content:

from anyio import Path, run


async def main():
    path = Path('/foo/bar')
    await path.write_bytes(b'hello, world')

run(main)

Asynchronously iterating a directory contents can be done as follows:

from anyio import Path, run


async def main():
    # Print the contents of every file (assumed to be text) in the directory /foo/bar
    dir_path = Path('/foo/bar')
    async for path in dir_path.iterdir():
        if await path.is_file():
            print(await path.read_text())
            print('---------------------')

run(main)