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Tue Sep 11 21:03:58 CEST 2012 · https://mail.python.org/pipermail/python-dev/2012-September/121668.html

Serhiy Storchaka, 11.09.2012 20:48:
> set([1, 2, 3]) => {1, 2, 3}
> set([x for ...]) => {x for ...}
> dict([(k, v) for ...]) => {k: v for ...}
> dict((k, v) for ...) => {k: v for ...}
> ''.join([s for ...]) => ''.join(s for ...)
> a.extend([s for ...]) => a.extend(s for ...)
> (f(x) for x in a) => map(f, a)
> (x.y for x in a) => map(operator.attrgetter('y'), a)
> (x[0] for x in a) => map(operator.itemgetter(0), a)
> (2 * x for x in a) => map((2).__mul__, a)
> (x in b for x in a) => map(b.__contains__, a)
> map(lambda x: x.strip(), a) => (x.strip() for x in a)
> x in ['i', 'em', 'cite'] => x in {'i', 'em', 'cite'}
> x == 'i' or x == 'em' or x == 'cite'] => x in {'i', 'em', 'cite'}
> a = []; for ...: a.append(x) => a = [x for ...]
> a = (); for ...: a.add(x) => a = {x for ...}
> a = {}; for ...: a[k] = v => a = {k: v for ...}
> for ...: f.write(...) => __fwrite = f.write; for ...: __fwrite(...)
> x = x + 1 => x += 1
> x = x + ' ' => x += ' '
> x = x + [y] => x.append(y)
> x = x + [y, z] => x.extend([y, z])
> 'x=%s' % repr(x) => 'x=%a' % (x,)
> 'x=%s' % x + s => 'x=%s%s' % (x, s)
> x = x + ', [%s]' % y => x = '%s, [%s]' % (x, y)
> range(0, x) => range(x)
> for i in range(len(a)): x = a[i] ... => for i, x in enumerate(a): ...
> i = 0; for x in a: i += 1 ... => for i, x in enumerate(a, 1): ...
> i = 1; for x in a: ... i += 1 => for i, x in enumerate(a, 1): ...
> s = 0; for ...: if ...: s += 1 => s = sum(1 for ... if ...)
> while True: s = f.readline(); if not s: break; ... => for s in f: ...
> def f(x): ... len() ... => def f(x, __len = len): ... __len() ...
> 
> Not all such transformations are always safe (and I know code in stdlib
> where they are not).

Actually, many of them are not, and some of them are even plain wrong or
may at least turn out not to be optimisations.

Stefan

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[Python-Dev] Release of astoptimizer 0.3