On Tue, Jan 12, 2010 at 7:14 PM, Oscar Gerardo Lazo Arjona <algebraicame...@gmail.com> wrote: > wouldn't it be a good idea to hard-code certain mathematical expressions > into sage > like pi, I , and e as sage additional keywords so that they could not be > variable names?
Yes. > I had a hard time figuring out what was happening when my e^x expression > didn't work > because i had made e into a string what do you think? The Python programming language doesn't easily support user-defined reserved expressions. However, in the Sage command line (IPython), and in the Sage notebook, as explained in the thread http://groups.google.com/group/sage-notebook/browse_thread/thread/6f2cd64ad21ff2a7/e96520862a228454?lnk=gst&q=fernando#e96520862a228454 one can *customize* the globals dictionary used in interactive evaluation of code. I think one could thus create a custom dictionary D so if you type e = 10 when Sage tries to do D['e'] = 10, the custom dict D would complain and raise an error. As a proof of concept, try pasting this into Sage: class MyDict(dict): def __setitem__(self, key, val): if key == 'e': raise NameError, "name %s is protected"%key dict.__setitem__(self, key, val) Then try this: sage: G = MyDict(globals()) sage: exec 'x=5; print x' in G 5 sage: G['x'] 5 sage: exec 'e=5; print e' in G Traceback (most recent call last): ... NameError: name e is protected sage: G['e'] e See how in the second case one isn't allowed to change e. Sage will soon have a similar mode so that undefined vars magically spring into existence *and* you can call methods using functional notation, which is what that thread linked to above is about. I do not think any of this should be on by *default*. However, it should be a simple option to turn any/all of this on with an easy short command. It would be helpful if somebody made a list of default protected variables. -- William
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