> Setting a new comprehension variable is not likely to be free, and may even be > more costly than calling f(x) twice if f() is a cheap expression: > > [x+1 + some_func(x+1) for x in range(10)] > > could be faster than > > [y + some_func(y) for x in range(10) let y = x + 1]
A bit of a nit — function call overhead is substantial in python, so if that is an actual function, rather than a simple expression, it’ll likely be slower to call it twice for any but trivially small iterables. > [(y, y**2) let y = x+1 for x in (1, 2, 3, 4)] Do we need the let? [ g(y) for y = f(x) for c in seq] Or, with expressions: [y + y**2 for y = x+1 for x in (1,2,3)] Maybe that would be ambiguous— I haven’t thought carefully about it. -CHB _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
