On Jan 22, 11:29 am, Martin Drautzburg <martin.drautzb...@web.de> wrote: > This has probably been asekd a million times, but if someone could give > a short answer anyways I's be most grateful.
Not sure there is exactly a short answer, and I am only qualified to maybe clarify some of the things you can and cannot do, not explain the reasons they are so. > What is it that allows one to write A.x? If I have a variable A, then > what to I have to assign to it to A.x becomes valid? Although not super concise, you'll find some good reading here: http://docs.python.org/tutorial/classes.html#a-word-about-names-and-objects It maybe does not address your question exactly, but it might give you insight into the overall philosophy. > Or even further: what do I have to do so I can write A.x=1 without > having done anything magical for x (but just for A)? I know you can do > this with classes, but not with plain objects, but why is that so? Here are examples where adding attributes on the fly does not work: Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) [GCC 4.3.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> s = '' >>> s.x = 1 Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'str' object has no attribute 'x' >>> d = {} >>> d.x = 1 Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'dict' object has no attribute 'x' >>> n = 0 >>> n.x = 1 Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'int' object has no attribute 'x' Here are examples when you can assign new attributes: >>> class C: pass ... >>> C.x = 1 >>> C().x = 1 >>> def f(): pass ... >>> f.x = 1 >>> lam = lambda n: n >>> lam.x = 1 Hope that helps or at least gets the discussion started. -- http://mail.python.org/mailman/listinfo/python-list
