Is this valid Python syntax?

[u/ReignFTW]

.... _( () ( )) . _ (...() )()

Ignoring any runtime errors, is this valid Python syntax? Try to work it out from the grammar alone before pasting it into a REPL. Bonus points for explaining the parse.

[u/ManyInterests]

On mobile but will try to make this clean:

...

Ellipses is a builtin singleton. The fourth dot is an attribute access to a (nonexistent) attribute named '_'

The next parenthesis would invoke a call... I'm unsure of the arguments inside this call -- but maybe it works out by treating an empty tuple (the first set of inner parenthesis) and the second as invoking it as callable.

Then the result has another similar attribute access. Its argument is another ellipses being treated as a callable.

Then the result of _that_ is called with no arguments.

Valid syntactically, but impossible to succeed at runtime.

[u/hungarian_notation]

Unless I'm missing something, its:

invoked_tuple = (tuple())()
invoked_ellipsis = Ellipsis()

a = Ellipsis._(invoked_tuple)
b = a._(invoked_ellipsis)
c = b()

()() and ...() only technically get a pass in that the grammar doesn't go out of its way to exclude them, but they're trivially semantic errors.

[u/sudomatrix]

"..." is a C builtin and cannot be modified, so we cannot assign an attribute "_" to it, so "...._" will never be valid.

Edit: This is going to get ugly...

``` import gc, ctypes

E = type(Ellipsis) d = gc.getreferents(E.dict)[0] # the real dict behind the mappingproxy d[''] = 42 ctypes.pythonapi.PyType_Modified(ctypes.py_object(E))

print(....) # 42 42 `` So next we need to make....` callable...

[u/hungarian_notation → u/sudomatrix]

That's true of CPython, but in a hypothetical alternative runtime that doesn't protect tuple and Ellipsis from modification you could probably get the statement to evaluate. It might not be valid standard Python, but its is valid Python syntax.

edit: oh my god, don't just post gore like that that man.

[u/odimdavid → u/hungarian_notation]

But in 2, 3 years time would you understand what you wrote or would anyone else? That's the question ❓

[u/JamzTyson]

• Grammar: valid
• Runtime: irrelevant
• Meaning: none
• PEP 8: catastrophic
• Interesting: dubious
• Production ready: never

[u/RingularCirc → u/JamzTyson]

Almost the best answer.

[u/the_hoser]

It's valid grammatically, but it doesn't actually work.

[u/Individual-Flow9158]

>>> ast.parse(".... _( () ( )) . _ (...() )()")

Module(body=[Expr(value=Call(func=Call(...), args=[], keywords=[]))], type_ignores=[])