Semantics of return statement in Python cell

[Tyler Caraza-Harter]

I was recently surprised by a return statement in the cell of a notebook I was reading, something like this (I simplified the original to highlight the strange behavior):

def f():
    pass


return 5

To my surprise, running this cell did not cause an exception.  Instead, 5 went to the Out.  Is this a bug, or is this behavior expected?

Surprisingly, I do get an error (SyntaxError: 'return' outside function) when I have a return without a proceeding function:

return 5

Thanks!

[Matthias Bussonnier]

That is an oversight and a bug in IPython, it is likely due to the fact that we attempt to parse top-level async-code.

We fixed similar bugs in recent IPython that allowed top level `break`, and `continue`.

This should raise a SyntaxError.

-- 

Matthias

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[Tyler Caraza-Harter]

Thanks for confirming!  Is this a known problem, or should I go ahead and report an issue on GitHub?  (I didn't see anything when I checked before, but I may have overlooked it).

[Matthias Bussonnier]

You can open one in https://github.com/ipython/ipython

The code that should handle that is here: https://github.com/ipython/ipython/blob/master/IPython/core/async_helpers.py#L94-L118

And we would need to figure out why it does not raise a SyntaxError.

-- 

M

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