Merge pull request #557 from realpython/python-async-iterators

Sample code for the article on async iterators

Author: brendaweles

python-async-iterators/README.md

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+# Asynchronous Iterators and Iterables in Python
+
+This folder provides the code examples for the Real Python tutorial [Asynchronous Iterators and Iterables in Python](https://realpython.com/python-async-iterators/).

python-async-iterators/async_comp.py

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+import asyncio
+
+
+async def async_range(start, end):
+    for i in range(start, end):
+        await asyncio.sleep(0.2)
+        yield i
+
+
+async def main():
+    number_list = [i async for i in async_range(0, 5)]
+    number_dict = {i: str(i) async for i in async_range(0, 5)}
+    print(number_list)
+    print(number_dict)
+
+
+asyncio.run(main())

python-async-iterators/async_csv.py

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+import asyncio
+import csv
+
+import aiofiles
+
+
+class AsyncCSVIterator:
+    def __init__(self, path):
+        self.path = path
+        self.file_was_read = False
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if not self.file_was_read:
+            async with aiofiles.open(self.path, mode="r") as file:
+                lines = await file.readlines()
+                self.reader = csv.reader(lines)
+                self.file_was_read = True
+        try:
+            return next(self.reader)
+        except StopIteration:
+            raise StopAsyncIteration
+
+
+async def main():
+    csv_iter = AsyncCSVIterator("data.csv")
+    # Skip the headers
+    await anext(csv_iter)
+    # Process the rest of the rows
+    async for row in csv_iter:
+        print(row)
+
+
+asyncio.run(main())

python-async-iterators/async_range_v1.py

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+import asyncio
+
+
+class AsyncRange:
+    def __init__(self, start, end):
+        self.start = start
+        self.end = end
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if self.start < self.end:
+            await asyncio.sleep(0.5)
+            value = self.start
+            self.start += 1
+            return value
+        else:
+            raise StopAsyncIteration
+
+
+async def main():
+    async for i in AsyncRange(0, 5):
+        print(i)
+
+
+asyncio.run(main())

python-async-iterators/async_range_v2.py

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+import asyncio
+
+
+class AsyncRange:
+    def __init__(self, start, end):
+        self.data = range(start, end)
+
+    async def __aiter__(self):
+        for i in self.data:
+            await asyncio.sleep(0.5)
+            yield i
+
+
+async def main():
+    async for i in AsyncRange(0, 5):
+        print(i)
+
+
+asyncio.run(main())

python-async-iterators/async_range_v3.py

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+import asyncio
+
+
+async def async_range(start, end):
+    for i in range(start, end):
+        await asyncio.sleep(0.5)
+        yield i
+
+
+async def main():
+    async for i in async_range(0, 5):
+        print(i)
+
+
+asyncio.run(main())

python-async-iterators/compress.py

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+import asyncio
+from pathlib import Path
+
+import aiofiles
+from zipstream import AioZipStream
+
+
+async def stream_generator(files):
+    async_zipstream = AioZipStream(files)
+    async for chunk in async_zipstream.stream():
+        yield chunk
+
+
+async def main(directory, zip_name="output.zip"):
+    files = [{"file": path} for path in directory.iterdir() if path.is_file()]
+    async with aiofiles.open(zip_name, mode="wb") as archive:
+        async for chunk in stream_generator(files):
+            await archive.write(chunk)
+
+
+directory = Path()
+asyncio.run(main(directory))

python-async-iterators/counter.py

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+import asyncio
+from random import randint
+
+
+class AsyncCounterIterator:
+    def __init__(self, name="", end=5):
+        self.counter = 0
+        self.name = name
+        self.end = end
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if self.counter >= self.end:
+            raise StopAsyncIteration
+        self.counter += 1
+        await asyncio.sleep(randint(1, 3) / 10)
+        return self.counter
+
+
+async def task(iterator):
+    async for item in iterator:
+        print(item, f"from iterator {iterator.name}")
+
+
+async def main():
+    # This code runs sequentially:
+    # await task(AsyncCounterIterator("#1"))
+    # await task(AsyncCounterIterator("#2"))
+
+    # This is concurrent:
+    await asyncio.gather(
+        task(AsyncCounterIterator("#1")),
+        task(AsyncCounterIterator("#2")),
+    )
+
+
+asyncio.run(main())

python-async-iterators/data.csv

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+Name,Age,Job
+John Doe,30,Software Engineer
+Jane Smith,25,Data Scientist
+Jim Brown,45,Project Manager
+Jessica Jones,40,UX Designer

python-async-iterators/inf_integers.py

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+import asyncio
+
+
+async def async_inf_integers(start=0):
+    current = start
+    while True:
+        yield current
+        current += 1
+        await asyncio.sleep(0.5)
+
+
+async def main(stop=5):
+    generator = async_inf_integers()
+    while True:
+        number = await anext(generator)
+        # Process the number here...
+        print(number)
+        if number == stop - 1:
+            break
+
+
+asyncio.run(main(20))