----- Original Message -----
> From: Chris Angelico <ros...@gmail.com> > To: > Cc: "python-list@python.org" <python-list@python.org> > Sent: Wednesday, February 4, 2015 3:24 PM > Subject: Re: meaning of: line, = > > On Thu, Feb 5, 2015 at 1:08 AM, ast <nom...@invalid.com> wrote: >> I dont understand why there is a comma just after line in the following >> command: >> >> line, = plt.plot(x, np.sin(x), '--', linewidth=2) >> >> >> I never saw that before >> >> Found here: >> > http://matplotlib.org/examples/lines_bars_and_markers/line_demo_dash_control.html >> > > That's a slightly unusual form of unpacking. Compare: > > def get_values(): > return 5, 7, 2 > > x, y, z = get_values() > > This is like "x = 5; y = 7; z = 2", because it unpacks the > function's > return value into those three targets. > > What you have is exactly the same, except that it has only one target. > So it's expecting plt.plot() to return an iterable with exactly one > thing in it, and it'll unpack it and put that thing into line: > > def get_packaged_value(): > return [42] > > x, = get_packaged_value() > > This is equivalent to "x = 42". I don't know matplotlib, so I > don't > know what it's returning or why, but as long as it's iterable and > yields exactly one thing, this will work. I have also never seen this before, but perhaps this: >>> f = lambda: [42] >>> result, = f() >>> result 42 ... is slightly cleaner than this: >>> result = f()[0] >>> result 42 -- https://mail.python.org/mailman/listinfo/python-list
