Re: Clearing globals in CPython
On 2014-10-01, Peter Otten __pete...@web.de wrote: Steven D'Aprano wrote: Out of curiosity, I ran: globals().clear() Oops. So, with no built-ins available, import no longer works. That makes things rather tricky. Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? $ python3 Python 3.4.0 (default, Apr 11 2014, 13:05:11) [GCC 4.8.2] on linux Type help, copyright, credits or license for more information. globals().clear() import that Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found object = 1 .__class__.__bases__[0] Quitter = [c for c in object.__subclasses__() if c.__name__ == Quitter][0] __builtins__ = Quitter.__call__.__globals__[__builtins__] import this The Zen of Python, by Tim Peters Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one-- and preferably only one --obvious way to do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than *right* now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea -- let's do more of those! I have funnier one :) $ python3 Python 3.4.1 (default, Sep 10 2014, 22:21:18) [GCC 4.9.1] on linux Type help, copyright, credits or license for more information. globals().clear() import this Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found True.__ True.__abs__( True.__dir__( True.__format__( True.__init__( True.__mul__( True.__radd__( True.__rlshift__( True.__rshift__(True.__sub__( True.__add__( True.__divmod__(True.__ge__( True.__int__( True.__ne__(True.__rand__( True.__rmod__( True.__rsub__( True.__subclasshook__( True.__and__( True.__doc__True.__getattribute__( True.__invert__(True.__neg__( True.__rdivmod__( True.__rmul__( True.__rtruediv__( True.__truediv__( True.__bool__( True.__eq__(True.__getnewargs__( True.__le__(True.__new__( True.__reduce__( True.__ror__( True.__rxor__( True.__trunc__( True.__ceil__( True.__float__( True.__gt__( True.__lshift__(True.__or__(True.__reduce_ex__( True.__round__( True.__setattr__( True.__xor__( True.__class__( True.__floor__( True.__hash__( True.__lt__(True.__pos__( True.__repr__( True.__rpow__( True.__sizeof__( True.__delattr__( True.__floordiv__( True.__index__( True.__mod__( True.__pow__( True.__rfloordiv__( True.__rrshift__( True.__str__( import this The Zen of Python, by Tim Peters Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one-- and preferably only one --obvious way to do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than *right* now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea -- let's do more of those! After invoking autocompletion (.__ and hitting tab), session has been automagically healed. -- jakubo -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On Mon, 06 Oct 2014 09:05:17 +, jakubo wrote: After invoking autocompletion (.__ and hitting tab), session has been automagically healed. That's ... um ... I have no words. Can you confirm that autocompletion modifies globals()? I don't have 3.4 installed here. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On Mon, Oct 6, 2014 at 8:08 PM, Steven D'Aprano st...@pearwood.info wrote: On Mon, 06 Oct 2014 09:05:17 +, jakubo wrote: After invoking autocompletion (.__ and hitting tab), session has been automagically healed. That's ... um ... I have no words. Can you confirm that autocompletion modifies globals()? I don't have 3.4 installed here. I can confirm that the trick does work. That's... extremely weird. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
Peter Otten wrote: Steven D'Aprano wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? $ python3 Python 3.4.0 (default, Apr 11 2014, 13:05:11) [GCC 4.8.2] on linux Type help, copyright, credits or license for more information. globals().clear() import that Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found object = 1 .__class__.__bases__[0] Quitter = [c for c in object.__subclasses__() if c.__name__ == Quitter][0] __builtins__ = Quitter.__call__.__globals__[__builtins__] import this The Zen of Python, by Tim Peters Nicely done! -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On 02/10/2014 09:11, Steven D'Aprano wrote: Peter Otten wrote: Steven D'Aprano wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? $ python3 Python 3.4.0 (default, Apr 11 2014, 13:05:11) [GCC 4.8.2] on linux Type help, copyright, credits or license for more information. globals().clear() import that Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found object = 1 .__class__.__bases__[0] Quitter = [c for c in object.__subclasses__() if c.__name__ == Quitter][0] __builtins__ = Quitter.__call__.__globals__[__builtins__] import this The Zen of Python, by Tim Peters Nicely done! Other than the Zen of Python what has Tim Peters ever done for us? Apart from... -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On 01/10/2014 18:00, Steven D'Aprano wrote: Out of curiosity, I ran: globals().clear() in the interactive interpreter. It broke much more than I expected! Built-ins were no longer available, and import stopped working. Interesting... :D Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? [].__class__.__module__ # It is a string... '__builtin__' So, I do not have any idea about how to get a module without importing something. Thanks for sharing :) -- Marco Buttu INAF-Osservatorio Astronomico di Cagliari Via della Scienza n. 5, 09047 Selargius (CA) Phone: 070 711 80 217 Email: mbu...@oa-cagliari.inaf.it -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On 2014-10-01, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? Python apparently _does_ need a restart command. -- Grant Edwards grant.b.edwardsYow! The PILLSBURY DOUGHBOY at is CRYING for an END to gmail.comBURT REYNOLDS movies!! -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On Fri, Oct 3, 2014 at 12:07 AM, Grant Edwards invalid@invalid.invalid wrote: On 2014-10-01, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? Python apparently _does_ need a restart command. Apparently not... you saw how easily Peter recovered :) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
Chris Angelico schrieb am 02.10.2014 um 16:12: On Fri, Oct 3, 2014 at 12:07 AM, Grant Edwards wrote: On 2014-10-01, Steven D'Aprano wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? Python apparently _does_ need a restart command. Apparently not... you saw how easily Peter recovered :) Right. All we need is a builtin function for that recovery code. Stefan -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On Thu, Oct 2, 2014 at 2:00 AM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? Oooh interesting. This is kinda like breaking out of a sandbox, and I know there are people here who are experts at that. However... I'm not entirely sure how to get a backtrace, when you don't have any built-in exceptions! In Python 2, I can define an old-style class and raise that. However, with the removal of __builtins__, Python throws a bunch of errors about restricted mode, so I'm really not sure where to go from there. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On Wed, Oct 1, 2014 at 9:14 AM, Chris Angelico ros...@gmail.com wrote: On Thu, Oct 2, 2014 at 2:00 AM, Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote: Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? Oooh interesting. This is kinda like breaking out of a sandbox, and I know there are people here who are experts at that. However... I'm not entirely sure how to get a backtrace, when you don't have any built-in exceptions! In Python 2, I can define an old-style class and raise that. However, with the removal of __builtins__, Python throws a bunch of errors about restricted mode, so I'm really not sure where to go from there. I've played with it a bit, and I haven't found any way to break it yet. I have discovered that you cannot directly declare classes, although you can access the type built-in (indirectly) so it might be possible to indirectly declare a class. It is also possible to access the types of many of the built-ins (str, bytes, dict, set, type, object, frame, function, code, generator, int, float at a minimum). Note that I've been playing with Python 3.4.1. -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
Steven D'Aprano wrote: Out of curiosity, I ran: globals().clear() in the interactive interpreter. It broke much more than I expected! Built-ins were no longer available, and import stopped working. I expected that global variables would be all lost, but built-ins would remain, since they don't live in the global namespace. I was wrong: globals().clear() x = len([]) Traceback (most recent call last): File stdin, line 1, in module NameError: name 'len' is not defined The reason, I think, is that CPython has a special __builtins__ global variable that the interpreter uses to access built-in functions. What *appears* to be happening is that if that __builtins__ global is missing, CPython can not access the built-ins. (Supporting this interpretation: IronPython, like CPython, has a __builtins__ global, and behaves the same when the globals() are cleared. Jython, which does not have a __builtins__ global, does not.) Well that's okay, I thought to myself, I'll just import the built-in functions: from builtins import len # use '__builtin__' in Python 2 Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found Oops. So, with no built-ins available, import no longer works. That makes things rather tricky. Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? $ python3 Python 3.4.0 (default, Apr 11 2014, 13:05:11) [GCC 4.8.2] on linux Type help, copyright, credits or license for more information. globals().clear() import that Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found object = 1 .__class__.__bases__[0] Quitter = [c for c in object.__subclasses__() if c.__name__ == Quitter][0] __builtins__ = Quitter.__call__.__globals__[__builtins__] import this The Zen of Python, by Tim Peters Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one-- and preferably only one --obvious way to do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than *right* now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea -- let's do more of those! -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On 01/10/2014 17:00, Steven D'Aprano wrote: Out of curiosity, I ran: globals().clear() in the interactive interpreter. It broke much more than I expected! Built-ins were no longer available, and import stopped working. I expected that global variables would be all lost, but built-ins would remain, since they don't live in the global namespace. I was wrong: globals().clear() x = len([]) Traceback (most recent call last): File stdin, line 1, in module NameError: name 'len' is not defined The reason, I think, is that CPython has a special __builtins__ global variable that the interpreter uses to access built-in functions. What *appears* to be happening is that if that __builtins__ global is missing, CPython can not access the built-ins. (Supporting this interpretation: IronPython, like CPython, has a __builtins__ global, and behaves the same when the globals() are cleared. Jython, which does not have a __builtins__ global, does not.) Well that's okay, I thought to myself, I'll just import the built-in functions: from builtins import len # use '__builtin__' in Python 2 Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found Oops. So, with no built-ins available, import no longer works. That makes things rather tricky. Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? We obviously need a Restart Command. -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence -- https://mail.python.org/mailman/listinfo/python-list
Re: Clearing globals in CPython
On 10/1/2014 12:00 PM, Steven D'Aprano wrote: Out of curiosity, I ran: globals().clear() in the interactive interpreter. It broke much more than I expected! Built-ins were no longer available, and import stopped working. As you discovered, this reduces the interpreter to a pure syntax machine with no name bindings -- sort of like a high-level assembler with no access to a function library. I expected that global variables would be all lost, but built-ins would remain, since they don't live in the global namespace. ... The reason, I think, is that CPython has a special __builtins__ global variable that the interpreter uses to access built-in functions. When executing statements from Shell, Idle restores __builtins__. globals().clear() print(dir()) ['__builtins__'] print(__builtins__) long listing The odd thing is that executing the same code from a file prints [] and then raises NameError: name '__builtins__' is not defined. Well that's okay, I thought to myself, I'll just import the built-in functions: from builtins import len # use '__builtin__' in Python 2 Traceback (most recent call last): File stdin, line 1, in module ImportError: __import__ not found Most keyword statements are implemented by internal functions not accessible from Python except through the statement syntax. Import is an exception. This is one of the hooks that allow the behavior of imports to be modified. The result is like, for instance, programming in C with 'include' disabled. Oops. So, with no built-ins available, import no longer works. That makes things rather tricky. Obviously the easiest way to recover is to exit the current session and restart it, but as a challenge, can we recover from this state? -- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
