Greg, Yes, what I describe may not be common and some code goes to serious lengths precisely to make direct connections to internals on an object hard to access.
But Python indeed allows and perhaps encourages you to use what you consider side effects but perhaps more. There are many dunder methods that allow all sorts of side effects or direct effects. You can set it up so an access of a variable increments a counter but perhaps it can set it up so three tries at guessing a password disables it or refuses to accept a number out of your bounds. Or it may be that some accesses to say write a value might also update several other values. For example, if you store a distance and also a time, any change of either one resets the value of a stored item holding a velocity. Perhaps adding additional values (or removing any) results in an immediate recalculation of the mean or standard deviation or whatever. If you allow direct access then you can make changes that get around that and I see no reason to assume programs do not use such ideas. Perhaps worse is that items may be dynamic. If an object representing me and my library card checks out a book, a new object may be created that holds the book. If you copy a pointer to the reference to the book in the library card object and later the book is returned and a new book checked out, then your reference is now pointing to the old book. If your goal is to get to the CURRENT book, you failed! So I stand by my suggestion that unless you know the code well and can be sure you won't corrupt things, this kind of convenient access has possible dangers. -----Original Message----- From: Greg Ewing <greg.ew...@canterbury.ac.nz> To: python-list@python.org Sent: Tue, Mar 22, 2022 7:12 pm Subject: Re: convenience On 23/03/22 7:00 am, Avi Gross wrote: > But are there costs or even errors > if you approach an inner part of an object directly? Can there be dunder > methods not > invoked that would be from the standard approach? What kind of inadvertent > errors can creep in? The attribute could be a property that returns different objects at different times depending on some condition. In that case you will need to think about whether you want the current value of the attribute, or the value it had when you looked it up before. Concerning dunder methods, there are a bunch of them involved in looking up an attribute of an object. Theoretically it's possible for these to have side effects and for bad things to happen if you skip them. But that would be very unusual and surprising, and we generally assume such things don't happen. -- Greg -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
