aiofiles is an Apache2 licensed library, written in Python, for handling local disk files in asyncio applications.
Ordinary local file IO is blocking, and cannot easily and portably made asynchronous. This means doing file IO may interfere with asyncio applications, which shouldn't block the executing thread. aiofiles helps with this by introducing asynchronous versions of files that support delegating operations to a separate thread pool.
async with aiofiles.open('filename', mode='r') as f:
contents = await f.read()
print(contents)
'My file contents'
Or, using the old syntax:
f = yield from aiofiles.open('filename', mode='r')
try:
contents = yield from f.read()
finally:
yield from f.close()
print(contents)
'My file contents'
- a file API very similar to Python's standard, blocking API
- support for buffered and unbuffered binary files, and buffered text files
- support for async/await (PEP 492) constructs
To install aiofiles, simply:
$ pip install aiofiles
Files are opened using the aiofiles.open()
coroutine, which in addition to
mirroring the builtin open
accepts optional loop
and executor
arguments. If loop
is absent, the default loop will be used, as per the
set asyncio policy. If executor
is not specified, the default event loop
executor will be used.
In case of success, an asynchronous file object is returned with an API identical to an ordinary file, except the following methods are coroutines and delegate to an executor:
close
flush
isatty
read
readall
read1
readinto
readline
readlines
seek
seekable
tell
truncate
writable
write
writelines
In case of failure, one of the usual exceptions will be raised.
The aiofiles.os
module contains executor-enabled coroutine versions of
several useful os
functions that deal with files:
stat
sendfile
When using Python 3.5 or greater, aiofiles file objects can be used as asynchronous context managers. Asynchronous iteration is also supported.
async with aiofiles.open('filename') as f:
async for line in f:
...
When using Python 3.3 or 3.4, be aware that the closing of a file may block,
and yielding from a coroutine while exiting from a context manager isn't
possible, so aiofiles file objects can't be used as (ordinary, non-async)
context managers. Use the try/finally
construct from the introductory
section to ensure files are closed.
When using Python 3.3 or 3.4, iteration is also unsupported. To iterate over a
file, call readline
repeatedly until an empty result is returned. Keep in
mind readline
doesn't strip newline characters.
f = yield from aiofiles.open('filename')
try:
while True:
line = yield from f.readline()
if not line:
break
line = line.strip()
...
finally:
yield from f.close()
Contributions are very welcome. Tests can be run with tox
, please ensure
the coverage at least stays the same before you submit a pull request.