On Mar 17, 11:49 am, [EMAIL PROTECTED] wrote: > What are the considerations in choosing between: > > return [a, b, c] > > and > > return (a, b, c) # or return a, b, c > > Why is the immutable form the default?
My understanding is that the immutable form is not the default - neither form is a default. The syntax for mutable lists requires square brackets. The syntax for immutable tuples only requires commas. However, commas are also used for other purposes. The parens for tuples are the same parens that might wrap any subexpression, in this case guarding against misinterpretation of commas. Since the parens are normally included for consistency as well as disambiguation, they end up being part of the tuple psychologically, but to Python itself they are separate. Personally, I'd make the parens compulsory so that mindsets and language specification are better aligned. If, that is, I was inventing a new language. But you can be sure that there's plenty of code out there that would break if a change like that was made now. As for choosing, if you never plan to modify the members of the sequence, a tuple expresses that intent and allows Python to enforce it. Some operations on tuples are probably also more efficient as a result. That said, 90%+ of the time I use a list either way. After all, as requirements change I might find I do need to modify after all. A change from tuple to list in any non-trivial case would require a thorough test suite to ensure that all cases are updated correctly (partly because Python is dynamically typed), and ashamed as I am to admit it, my test suites are rarely that thorough. Without that testing, there might be an obscure case where you still create a tuple, and that tuple gets passed to code that expects a list and tries to replace an element. -- http://mail.python.org/mailman/listinfo/python-list
