On Tuesday, June 14, 2016 at 8:13:53 AM UTC+5:30, Steven D'Aprano wrote: > No. The sun exploding was me gently mocking you for your comment disputing > the "unconditional" part. Yes, you are technically right that technically > the "else" block will only run if no "break" is reached, and no "return" is > reached, no exception is raised, also that os._exit or os.abort aren't > called, the CPU doesn't catch fire, and the world isn't destroyed. > > If we try to enumerate all the things which could prevent the "else" block > from running, we'll be here for decades. But, and this is the point that > everyone seems to have missed, * every single one of those things* is > completely independent of the for...else statement. > > *Including* the presence or absence of a "break".
This is real wild: A break that is inside a for is independent of the for?!?! Thats about as meaningful a statement as saying that the algebraic expression "x² + 1" has a value independent of "x" However see below > > If you want to understand how Python statements work, you should understand > them in isolation (as much as possible), which then allows you to > extrapolate their behaviour in combination with other statements. Most > lines of Python code are understandable in isolation, or at least close to > isolation. You can get *very close* to a full understanding of Python by > just reading one line at a time (with perhaps a bit of short term memory to > remember if you are compiling a function, building a class, etc). > > E.g. you don't need to understand for loops to understand if...else. > > And vice versa: for...else has a well-defined meaning and operates in a > simple fashion in isolation of other language features. Its not compulsory > to put a "return" statement inside your for loop. Nor is it compulsory to > put a "raise" inside it. And "break" is not compulsory either. This *desire* for what you call isolation is a standard tenet of semantics and is right It is called compositionality Inn programming: https://en.wikipedia.org/wiki/Denotational_semantics#Compositionality More general linguistics: https://en.wikipedia.org/wiki/Principle_of_compositionality However gotos break compositionality unless one introduces heavy artillery like continuations And break is a euphemism for goto -- https://mail.python.org/mailman/listinfo/python-list
