Gary Herron wrote: > Robert Kern wrote: ... >> Use "is" when you really need to compare by object identity and not >> value. > > But that definition is the *source* of the trouble. It is *completely* > meaningless to newbies. Until one has experience in programming in > general and experience in Python in particular, the difference between > "object identity" and "value" is a mystery.
Then teach them the difference, rather than give them bogus advice. > So in order to lead newbies away from this *very* common trap they often > fall into, it is still a valid rule to say > > Newbies: Never use "is" to compare immutable types. Look in the standard library, and you will see dozens of cases of first-quality code breaking your "valid" rule. Your rule is not valid. A better rule might be: Never use "is" to compare equality. Or even: Never use "is" unless you know the difference between identity and equality. Or even: Only use "is" on Tuesdays. At least that last rule is occasionally right (in the same way a stopped clock is right twice a day), while your rule is *always* wrong. It is never correct to avoid using "is" when you need to compare for identity. > of even better > > Newbies: Never use "is" to compare anything. Worse and worse! Now you're actively teaching newbies to write buggy code! -- Steven -- http://mail.python.org/mailman/listinfo/python-list
