How could I asynchronously read a specific line of a file with trio

Question

So I'd like to open files with trio (asynchronously) and then as the file is rather large read a single specific line of it

So in "normal" synchronous python, I'd do something like this:

with open("text.txt") as f:
    for i, line in enumerate(f):
        if i == 3:
            print(line)

This would print the content of a file's second line

Now issue is, when using trio's open_file method, enumerate(f) returns the error: TypeError: 'AsyncIOWrapper' object is not iterable

And following the docs:

async with await trio.open_file("text.txt") as f:
    async for i, line in f:
        print(i)
        print(line)

will only return the line's value for i, and just whitespace for line

And so, how would one go to read a specific line of a large file without losing to much memory with trio/asynchronoulsy?

Answer 1

Building a async enumerate function as such:

async def aenumerate(ait, start=0):
    i = start
    async for item in ait:
        yield i, item
        i += 1

then you can easily do as follows:

async with await trio.open_file("text.txt") as f:
    async for i, line in aenumerate(f):
        print(i)
        print(line)