On Sun, Sep 20, 2009 at 11:16 AM, Peng Yu <pengyu...@gmail.com> wrote: > On Sun, Sep 20, 2009 at 9:19 AM, Dave Angel <da...@ieee.org> wrote: >> Peng Yu wrote: >>> >>> <snip> >>>> >>>> you might use: >>>> >>> >>> Is __repr__ =_str__ copy by reference or by value? If I change >>> __str__ later on, will __repr__ be changed automatically? >>> >>> Regards, >>> Peng >>> >>> >> >> Reference or value? Neither one. This assignment is no different than any >> other attribute assignment in Python. Technically, it binds the name >> __repr__ to the function object already bound by __str__. You now have a >> second name pointing to the same object. Rebinding one of those names to >> yet another different object won't affect the other name. >> >> name1 = "this is a test" >> name2 = name1 >> name1 = "another string" #this has no effect on name2 >> >> print name1, name2 > > I am more familiar with C++ than python. So I need to connect python > concept to C++ concept so that I can understand it better. > > name1 and name are all references (in the C++ sense), right? > > __repr__ and __str__ are references (in the C++ sense) to functions > and both of them could refer to the same function or two different > ones, right? >
Sort of, but it would be best to forget about the C++ ideas of references and values because it will only confuse you. In python, everything is an object and every attribute is stored as a dict key, including functions. When you do __repr__ = __str__, you are making the name '__repr__' refer to the same object as the name '__str__'. Since they are the same object, any mutations made to one object will appear in the other. However, a reassignment does not change the value of the object, it just makes that key refer to another object. So if you were to later change __str__ to a different method, __repr__ wouldn't change. > Regards, > Peng > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
