On Fri, May 30, 2014 at 9:27 PM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > This is why I'm so adamant that, while REPLs may be permitted to > introduce *new* syntax which is otherwise illegal to the Python parser, > (e.g. like IPython's %magic and !shell commands) they *must not* change > the meaning of otherwise legal Python syntax. It's simply a bad idea to > have legal Python code mean different things depending on what > environment you're running it in.
Hmm. I'm not sure that "raises SyntaxError" is any less a part of the language's promise than "evaluates to twice the value of x" is. Would you, for instance, permit the REPL to define a new __future__ directive, on the basis that it's invalid syntax currently? >>> from __future__ import magic_command_history SyntaxError: future feature magic_command_history is not defined I don't think SyntaxError equates to "invitation to make changes". Also, consider: >>> for i in range(5): i*3+2 2 5 8 11 14 If you do this in a script, it's perfectly legal, but won't print anything. So the REPL is already "chang[ing] the meaning of otherwise legal Python syntax", and what's more, it's making None into a special case: >>> for i in range(5): None if i%2 else i 0 2 4 Practicality beats purity. If it's more useful to the end user for something valid-but-illogical to have a new bit of meaning in interactive mode, I say go for it. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
