gh-122461: Document that compile() and ast.parse() raise SyntaxError for null bytes

[devdanzin]

Update docs for compile() and ast.parse() because they raise SyntaxError instead of ValueError for null bytes since #97594.

• Issue: Incorrect information about exception raised if source contains null bytes for ast.parse() and compile() #122461

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📚 Documentation preview 📚: https://cpython-previews--122462.org.readthedocs.build/

[devdanzin]

Requesting review from @JelleZijlstra.

[devdanzin]

Thank you both for the reviews!

[serhiy-storchaka]

Note that UnicodeEncodeError (which is a subclass of ValueError) can still be raised if the source string is not encodable.

[serhiy-storchaka]

There are also mentions of ValueError in the codeop documentation and docstrings. I do not know whether they are still valid.

[devdanzin]

Note that UnicodeEncodeError (which is a subclass of ValueError) can still be raised if the source string is not encodable.

Yes, for code such as ast.parse("\ud800"). Should this possibility be added to the documentation?

Plus MemoryError and RecursionError are possible for too deeply nested code.

[serhiy-storchaka]

OverflowError is documented in codeop, and it can still be raised. For example:

>>> import ast
>>> try: ast.parse('x'*2**31, '?', 'exec')
... except BaseException as err: e = err
... 
>>> str(e)
'Parser column offset overflow - source line is too big'
>>> type(e)
<class 'OverflowError'>

I do not know whether ValueError other than UnicodeEncodeError can be raised, but it is safer to document ValueError, OverflowError and RecursionError in all these places. I do not think that it is worth to document MemoryError or say KeyboardInterrupt specially, because they depend rather on the environment than on the input and you cannot fix them.

[devdanzin]

Would this count?

>>> ast.parse("", feature_version=(2,2))
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    ast.parse("", feature_version=(2,2))
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "~\PycharmProjects\cpython\Lib\ast.py", line 50, in parse
    raise ValueError(f"Unsupported major version: {major}")
ValueError: Unsupported major version: 2

Edit: here's another one:

>>> ast.parse("", "\0")
Traceback (most recent call last):
  File "<python-input-9>", line 1, in <module>
    ast.parse("", "\0")
    ~~~~~~~~~^^^^^^^^^^
  File "~\PycharmProjects\cpython\Lib\ast.py", line 53, in parse
    return compile(source, filename, mode, flags,
                   _feature_version=feature_version, optimize=optimize)
ValueError: embedded null character

[python-cla-bot]

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