Materials for Python 3.14 Preview: Better Syntax Error Messages

Author: bzaczynski

python314-preview-errors/README.md

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+# Python 3.14 Preview: Better Syntax Error Messages
+
+The materials contained in this folder are designed to complement the Real Python tutorial [Python 3.14 Preview: Better Syntax Error Messages](https://realpython.com/python314-error-messages/).

python314-preview-errors/errors.py

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+import sys
+import textwrap
+
+MAX_WIDTH = 80
+
+
+def main() -> None:
+    for title, snippets in get_scenarios().items():
+        print_headline(title)
+        for snippet in snippets:
+            execute(snippet)
+
+
+def get_scenarios() -> dict[str, list[str]]:
+    return {
+        "Keyword Typos": [
+            "forr i in range(5):",
+            "why True:",
+        ],
+        "Strict elif After else": [
+            """
+                if x > 0:
+                    print("positive")
+                else:
+                    print("not positive")
+                elif x == 0:  # This is invalid
+                    print("zero")
+            """,
+        ],
+        "Conditional Expressions": ["1 if True else pass"],
+        "String Closures": [
+            'message = "She said "Hello" to everyone"',
+        ],
+        "String Prefix Combinations": ['text = fb"Binary {text}"'],
+        "Unpacking Assignments": [
+            'dog, age, city, hobbies = ["Frieda", 8, "Berlin"]',
+            'dog, age = ["Frieda", 8, "Berlin"]',
+        ],
+        "Aliases": ["import sys as [alias]"],
+        "Unhashable Types": ['grid = {[0, 0]: "Label", [0, 1]: "Input"}'],
+        "Math Domain": [
+            """
+                import math
+                math.sqrt(-1)
+            """
+        ],
+        "Context Managers": [
+            """
+                import asyncio
+                async def process_data():
+                    with asyncio.TaskGroup() as tg:
+                        pass
+                
+                asyncio.run(process_data())
+            """,
+            """
+                import asyncio
+                async def read_file():
+                    async with open(__file__) as f:
+                        return f.read()
+                        
+                asyncio.run(read_file())
+            """,
+        ],
+    }
+
+
+def print_headline(text: str, width: int = MAX_WIDTH) -> None:
+    print(f" {text} ".center(width, "="))
+
+
+def execute(source_code: str) -> None:
+    raw_source_code = dedent(source_code)
+    try:
+        print(with_repl_prompts(raw_source_code))
+        exec(raw_source_code, globals())
+    except (SyntaxError, ValueError, TypeError) as e:
+        sys.excepthook(type(e), e, e.__traceback__)
+    finally:
+        print()
+
+
+def with_repl_prompts(source_code: str) -> str:
+    return "\n".join(
+        (">>> " if i == 0 else "... ") + line
+        for i, line in enumerate(source_code.splitlines())
+    )
+
+
+def dedent(source_code: str) -> str:
+    return textwrap.dedent(source_code).strip("\n")
+
+
+if __name__ == "__main__":
+    main()