Modern APIs with FastAPI and Python Transcripts
Chapter: Modern language foundations
Lecture: Concept: An async method
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We saw how powerful asynchronous methods can be.
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Let's just take a moment and review some of the core ideas around building async
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methods. Normally, we define a method like "get HTML" as "def get_HTML"
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but if you want it to be asynchronous,
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you say "async def get_HTML" right.
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We're gonna be doing that within FastAPI all over the place.
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And then we have this somewhat unusual construct called an "async with block"
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and that's probably the most unusual thing in async amd await.
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And what we're going to do there is the actual with Block is opening a network
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connection, opening a socket, and so we want to do that asynchronously.
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It actually takes a little bit of time
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if you just create these separately without the async stuff,
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it's quite a bit slower. So this lets us open all the sockets at the
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same time, and then we're gonna issue some of these requests.
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We're gonna say "client.get". Now
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normally, that's just a blocking call and you get a value back.
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But when you call an asynchronous method,
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which client.get is, what you get back is not the return value.
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It didn't even actually run. What you get back is something called a co-routine
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that if you await it, it will run and give you the value.
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So here, we're going to say,
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"await client.get", get the response,
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and then we just work with it normal.
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The big takeaway here is that where you see "async with", where you see
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the word "await", all of those points,
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if you're waiting on some external system, your program, in this case,
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the web scraper, more generally, probably the API server, will be able to
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actually handle other requests and do other work
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until this client gets back to us with its answer,
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then we pick it up and run with it.
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Often, people think of this async await as scaling the computation or like adding
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threads. Threads are not even really involved.
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What it lets you do is it says it lets you mark different places in your
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function that says "I'm waiting on something other than our program.
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I'm waiting on something external, you can go to other work until that gets back
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to us" right? So here we're waiting on the talkpython.fm server,
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could be a database, it could be something else.
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So it's this async with and await where we're marking,
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like, "here you can go to other work until I get this response and then
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please start me up and we'll keep running".
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And that's how async and await works,
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and because most Web applications are waiting on something else,
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they're talking to databases, waiting on them,
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they're talking to other API's, micro services,
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and so on, waiting on them,
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you can do a whole lot more work
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if you can find a way for your Web server
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to allow it to work on other stuff while it's waiting,
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and that's exactly what async and await does for us.