Sample code for: Python 3.15 Preview: UTF-8 by Default (#797)

* Sample code for: Python 3.15 Preview: UTF-8 by Default

* Rename example files descriptively and print entry count in app_v2

* Add data files read by the sample scripts

Ship data.json, legacy.csv, and notes.txt so every script runs on first
try instead of raising FileNotFoundError. Also align the os_encoding.py
comment with the tutorial's lowercase "UTF-8 mode".

* Keep app.py parsing JSON after adding the explicit encoding

app_v2.py read the file as raw text, so len(data) counted characters and
printed "Loaded 29 entries". Restore json.load() so the only difference
from app_v1.py is the encoding argument, matching the tutorial.

* Parse data.json with json.load() in explicit_encoding.py

Keeps data.json handling consistent with app_v1.py and app_v2.py across
the tutorial's examples. legacy.csv stays a raw read, since the point
there is the locale sentinel rather than parsing.

---------

Co-authored-by: Bartosz Zaczyński <bartosz.zaczynski@gmail.com>

Author: lpozo

python315-utf8-default/README.md

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+# Python 3.15 Preview: UTF-8 by Default
+
+This folder provides the code examples for the Real Python tutorial [Python 3.15 Preview: UTF-8 by Default](https://realpython.com/python315-utf8-default/)

python315-utf8-default/app_v1.py

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+import json
+
+with open("data.json") as f:
+    data = json.load(f)
+
+print(f"Loaded {len(data)} entries")

python315-utf8-default/app_v2.py

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+import json
+
+from constants import ENCODING
+
+with open("data.json", encoding=ENCODING) as f:
+    data = json.load(f)
+
+print(f"Loaded {len(data)} entries")

python315-utf8-default/constants.py

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+ENCODING = "utf-8"  # Single source of truth for text I/O

python315-utf8-default/data.json

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+{"café": "☕", "naïve": true}

python315-utf8-default/explicit_encoding.py

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+import json
+
+with open("data.json", encoding="utf-8") as f:  # Portable and unambiguous
+    data = json.load(f)
+
+with open("legacy.csv", encoding="locale") as f:  # Intentional locale use
+    legacy = f.read()

python315-utf8-default/legacy.csv

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+id,name,quantity
+1,espresso,12
+2,americano,8
+3,macchiato,5

python315-utf8-default/locale_encoding.py

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+with open("legacy.csv", encoding="locale") as f:
+    legacy = f.read()

python315-utf8-default/main.py

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+import textlib
+
+textlib.read_text("notes.txt")

python315-utf8-default/notes.txt

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+Remember to pass an explicit encoding to every text-mode open() call.