Merge pull request #676 from realpython/python-with-statement

Sample code for the article on the `with` statement

Author: brendaweles

python-with-statement/README.md

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+# Python's with Statement: Manage External Resources Safely
+
+This folder provides the code examples for the Real Python tutorial [Python's with Statement: Manage External Resources Safely](https://realpython.com/python-with-statement/).

python-with-statement/exc_handling.py

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+class HelloContextManager:
+    def __enter__(self):
+        print("Entering the context...")
+        return "Hello, World!"
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        print("Leaving the context...")
+        if isinstance(exc_value, IndexError):
+            # Handle IndexError here...
+            print(f"An exception occurred in your with block: {exc_type}")
+            print(f"Exception message: {exc_value}")
+            return True
+
+
+with HelloContextManager() as hello:
+    print(hello)
+    hello[100]
+
+print("Continue normally from here...")

python-with-statement/hello.py

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+class HelloContextManager:
+    def __enter__(self):
+        print("Entering the context...")
+        return "Hello, World!"
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        print("Leaving the context...")
+        if isinstance(exc_value, IndexError):
+            print(f"An exception occurred in with block: {exc_type}")
+            print(f"Exception message: {exc_value}")
+            return True
+        return False
+
+
+with HelloContextManager() as hello:
+    print(hello)
+    # hello[100]
+
+print("Continue normally from here...")

python-with-statement/indenter.py

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+class Indenter:
+    def __init__(self):
+        self.level = -1
+
+    def __enter__(self):
+        self.level += 1
+        return self
+
+    def __exit__(self, *_):
+        self.level -= 1
+
+    def print(self, text):
+        print("    " * self.level + text)

python-with-statement/precision.py

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+from decimal import Decimal, localcontext
+
+with localcontext(prec=42):
+    print(Decimal("1") / Decimal("42"))
+
+
+print(Decimal("1") / Decimal("42"))

python-with-statement/redirect.py

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+import sys
+
+
+class StandardOutputRedirector:
+    def __init__(self, new_output):
+        self.new_output = new_output
+
+    def __enter__(self):
+        self.std_output = sys.stdout
+        sys.stdout = self.new_output
+
+    def __exit__(self, *_):
+        sys.stdout = self.std_output

python-with-statement/scan_directory.py

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+import os
+
+with os.scandir(".") as dir_entries:
+    for entry in dir_entries:
+        print(entry.name, "->", entry.stat().st_size, "bytes")

python-with-statement/site_checker_v1.py

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+import asyncio
+
+import aiohttp
+
+
+async def check(url):
+    async with aiohttp.ClientSession() as session:
+        async with session.get(url) as response:
+            print(f"{url}: status -> {response.status}")
+            html = await response.text()
+            print(f"{url}: type -> {html[:17].strip()}")
+
+
+async def main():
+    await asyncio.gather(
+        check("https://realpython.com"),
+        check("https://pycoders.com/"),
+    )
+
+
+asyncio.run(main())

python-with-statement/site_checker_v2.py

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+import asyncio
+
+import aiohttp
+
+
+class AsyncSession:
+    def __init__(self, url):
+        self._url = url
+
+    async def __aenter__(self):
+        self.session = aiohttp.ClientSession()
+        response = await self.session.get(self._url)
+        return response
+
+    async def __aexit__(self, *_):
+        await self.session.close()
+
+
+async def check(url):
+    async with AsyncSession(url) as response:
+        print(f"{url}: status -> {response.status}")
+        html = await response.text()
+        print(f"{url}: type -> {html[:17].strip()}")
+
+
+async def main():
+    await asyncio.gather(
+        check("https://realpython.com"),
+        check("https://pycoders.com"),
+    )
+
+
+asyncio.run(main())

python-with-statement/timer.py

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+from time import perf_counter, sleep
+
+
+class Timer:
+    def __enter__(self):
+        self.start = perf_counter()
+
+    def __exit__(self, *_):
+        end = perf_counter()
+        print(f"Elapsed time: {end - self.start:.4f} seconds")
+
+
+with Timer():
+    # The code to measure goes here...
+    sleep(0.5)