On Sat, May 01, 2021 at 03:05:51AM -0000, Valentin Berlier wrote:
It's kind of weird that people seem to be missing the point about this. Python already has comprehensions for all the iterable builtins except strings.
No it doesn't. I count 15 builtin iterables, only three have comprehensions.
The argument that we can already do this with the "".join() idiom is backwards. It's something we have to do _because_ there's no way to write a string comprehensions directly. Comprehensions express intent.
Okay. What string comprehension do I write to express my intent to write a string containing words separated by commas? What string comprehension do I write to express my intent to write a string containing lines separated by newlines? What string comprehension do I write to express my intent to write a string containing substrings separated by ' - ' (space, hyphen, space)? `str.join` can express the intent of every single one of those, as well as the intent to write a string containing substrings separated by the empty string.
Joining a generator expression with an empty string doesn't convey the intent that you're building a string where each character is derived from another iterable.
Of course it does. What else could `''.join(expression)` mean, if not to build a string with the substrings derived from expression separated by the empty string?
Also I haven't seen anyone acknowledge the potential performance benefits of string comprehensions. The "".join() idiom needs to go through the entire generator machinery to assemble the final string, whereas a decent implementation of string comprehensions would enable some pretty significant optimizations.
Do you know what's worse than premature optimization? Accepting a new special-case language feature on the basis that, maybe some day, it might possibly enable a premature optimization. If you're going to claim a micro-optimization benefit, I think you need more than just to hand-wave that "a decent implementation" would allow it. Let's start with the simplest case: c'substring for substring in expression' What optimizations are available for that? -- Steve