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Can global variable be passed into Python function?

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  Can global variable be passed into Python function? Sam <lightaiyee@gmail.com> - 2014-02-20 22:37 -0800
    Re: Can global variable be passed into Python function? dieter <dieter@handshake.de> - 2014-02-21 08:23 +0100
      Re: Can global variable be passed into Python function? Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-02-21 10:55 +0200
        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-21 12:10 +0200
    Re: Can global variable be passed into Python function? Peter Otten <__peter__@web.de> - 2014-02-21 08:34 +0100
    Re: Can global variable be passed into Python function? Gary Herron <gary.herron@islandtraining.com> - 2014-02-21 00:41 -0800
    Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-21 08:55 +0000
    Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-21 07:13 -0500
      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-21 14:52 +0200
      Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 03:28 +0000
        Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-21 22:45 -0500
          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 06:29 +0000
    Re: Can global variable be passed into Python function? Travis Griggs <travisgriggs@gmail.com> - 2014-02-21 09:59 -0800
    Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 05:16 +1100
      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-21 21:20 +0200
        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 17:36 +1100
          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 07:18 +0000
            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 18:29 +1100
              Re: Can global variable be passed into Python function? wxjmfauth@gmail.com - 2014-02-22 00:02 -0800
                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 19:10 +1100
                  Re: Can global variable be passed into Python function? wxjmfauth@gmail.com - 2014-02-22 00:26 -0800
                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 08:28 +0000
              Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 08:35 +0000
                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 19:45 +1100
                Re: Can global variable be passed into Python function? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-24 21:07 +1300
                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-24 15:57 +0000
                    Re: Can global variable be passed into Python function? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-02-24 21:12 -0500
                    Re: Can global variable be passed into Python function? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-26 23:59 +1300
                      Re: Can global variable be passed into Python function? MRAB <python@mrabarnett.plus.com> - 2014-02-26 18:59 +0000
        Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 06:57 +0000
          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-22 09:28 +0200
            Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-22 08:45 +0000
              Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-22 19:54 +1100
    Python and variables (was: Can global variable be passed into Python function?) Ben Finney <ben+python@benfinney.id.au> - 2014-02-22 11:13 +1100
    Re: Can global variable be passed into Python function? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-02-21 21:47 -0500
    Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-21 22:14 -0500
    Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-22 14:15 +0000
      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-22 16:44 +0200
      Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-23 01:39 +0000
        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-23 12:50 +1100
          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-23 06:20 +0000
            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-23 18:23 +1100
        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-23 11:52 +0200
          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-23 10:30 +0000
          Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-23 21:32 +1100
            Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-23 13:01 +0200
              Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-23 22:12 +1100
                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-23 17:24 +0200
                  Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-24 02:41 +1100
                    Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-23 23:04 +0200
                      Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-23 21:18 +0000
              Re: Can global variable be passed into Python function? Terry Reedy <tjreedy@udel.edu> - 2014-02-23 12:06 -0500
                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-23 23:10 +0200
                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-24 00:37 +0000
                    Re: Can global variable be passed into Python function? wxjmfauth@gmail.com - 2014-02-24 01:35 -0800
              Re: Can global variable be passed into Python function? j.e.haque@gmail.com - 2014-02-24 10:05 -0800
                Re: [OT] Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-02-24 11:19 -0700
                  Re: [OT] Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-02-24 19:42 +0000
                    Re: [OT] Can global variable be passed into Python function? Dave Angel <davea@davea.name> - 2014-03-01 23:02 -0500
                      Re: [OT] Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-03-02 16:45 +0000
                        Re: [OT] Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 16:55 +0000
                        Re: [OT] Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-03 06:24 +1100
                          Re: [OT] Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-03-03 14:18 +0000
                            Re: [OT] Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-04 01:25 +1100
                    Re: [OT] Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 15:17 +1100
                    Re: [OT] Can global variable be passed into Python function? Dave Angel <davea@davea.name> - 2014-03-02 08:22 -0500
                    Re: [OT] Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-03 00:57 +1100
                    Re: [OT] Can global variable be passed into Python function? Dave Angel <davea@davea.name> - 2014-03-02 14:17 -0500
                    Re: [OT] Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-03 06:32 +1100
                    Re: [OT] Can global variable be passed into Python function? Dave Angel <davea@davea.name> - 2014-03-02 17:58 -0500
                Re: Can global variable be passed into Python function? random832@fastmail.us - 2014-02-24 13:20 -0500
                Re: [OT] Can global variable be passed into Python function? random832@fastmail.us - 2014-02-24 13:21 -0500
                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-25 05:22 +1100
                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-25 05:25 +1100
                Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-24 20:00 +0000
    Re: Can global variable be passed into Python function? Dave Angel <davea@davea.name> - 2014-02-22 10:02 -0500
    Re: Can global variable be passed into Python function? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-02-22 13:03 -0500
      Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-23 00:39 +0000
      Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-02-22 19:57 -0500
    Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 05:24 -0800
      Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-27 12:54 -0500
        Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 15:29 -0800
          Re: Can global variable be passed into Python function? Steven D'Aprano <steve@pearwood.info> - 2014-02-28 02:07 +0000
            Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 18:29 -0800
              Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 15:43 +1100
                Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 21:39 -0800
                  Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 16:53 +1100
                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 09:43 +0200
                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve@pearwood.info> - 2014-02-28 08:23 +0000
                    Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-02-28 19:46 +1100
                      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 12:02 +0200
                        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 21:55 +1100
                          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 13:30 +0200
                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 22:51 +1100
                              Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 14:25 +0200
                                Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 00:22 +0000
                        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 22:08 +1100
                          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 13:38 +0200
                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 23:22 +1100
                            Re: Can global variable be passed into Python function? Neil Cerutti <neilc@norwich.edu> - 2014-02-28 13:47 +0000
                              Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 16:26 +0200
                                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 01:37 +1100
                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 17:29 +0200
                                    Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 02:46 +1100
                                    Re: Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-02-28 16:09 +0000
                                      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 10:00 +0200
                                Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-02-28 09:43 -0500
                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 10:00 +0200
                                    Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 17:26 +0200
                                      Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-03-02 10:34 -0500
                                        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 17:52 +0200
                                          Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-03 03:23 +1100
                                          Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 16:53 +0000
                            Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-28 15:06 +0000
                        Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-28 15:50 +0000
                          Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 10:04 -0800
                            Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 20:53 +0200
                              Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 05:59 +1100
                                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 21:20 +0200
                                  Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 12:22 -0800
                                    Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-02-28 23:03 +0200
                                      Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-28 21:23 +0000
                                        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 01:06 +0200
                                          Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 11:02 +1100
                                            Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-02-28 19:48 -0500
                                          Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 13:00 +1100
                                            Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-02-28 22:15 -0500
                                          Re: Can global variable be passed into Python function? albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-03-10 14:12 +0000
                                            Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-10 16:29 +0200
                                        Re: Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-02-28 22:00 +0000
                                          Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-02 09:36 +1100
                                            Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-01 14:50 -0800
                                      Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 15:36 -0800
                                        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 02:32 +0200
                                        Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-28 19:40 -0500
                                          Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 17:08 -0800
                                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 13:01 +1100
                                              Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 21:30 -0800
                                                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 17:24 +1100
                                                  Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-01 13:40 -0800
                                                    Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 22:01 +0000
                                                      Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-01 14:07 -0800
                                                        Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 23:21 +0000
                                                          Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-01 16:23 -0800
                                                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 11:28 +1100
                                                            Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 00:36 +0000
                                                            Re: Can global variable be passed into Python function? Ned Deily <nad@acm.org> - 2014-03-01 16:55 -0800
                                                            Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 01:15 +0000
                                                    Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 09:11 +1100
                                            Re: Can global variable be passed into Python function? Ned Batchelder <ned@nedbatchelder.com> - 2014-02-28 21:15 -0500
                                              Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 20:36 -0800
                                        Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 01:07 +0000
                                        Re: Can global variable be passed into Python function? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-03-01 16:10 +1300
                                        Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-02-28 19:02 -0500
                                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-28 23:33 +0000
                                  Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 12:50 +1100
                              Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-28 23:04 +0000
                                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 02:03 +0200
                                  Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 00:44 +0000
                                    Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 03:06 +0200
                                      Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 01:59 +0000
                                        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 13:03 +1100
                                          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 03:29 +0000
                                        Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 12:39 +0200
                                  Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 01:10 +0000
                                    Re: Can global variable be passed into Python function? "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 17:29 -0800
                        Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 10:17 +1100
                          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 02:11 +0200
                            Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 11:50 +1100
                              Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 03:10 +0200
                                Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 01:19 +0000
                                Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 12:41 +1100
                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 12:31 +0200
                                    Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 21:48 +1100
                                      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 13:28 +0200
                                        Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-01 22:59 +1100
                                          Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 17:07 +0000
                                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 04:27 +1100
                                            Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 20:25 +0200
                                              Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-02 09:30 +1100
                                              Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 23:13 +0000
                                        Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-02 00:03 +1100
                                          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 19:23 +0200
                                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 04:30 +1100
                                            Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-02 09:34 +1100
                                              Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 10:03 +0200
                                                Re: Can global variable be passed into Python function? Ben Finney <ben+python@benfinney.id.au> - 2014-03-02 21:59 +1100
                                                Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 13:00 +0000
                                        Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-01 15:15 +0000
                                        Re: Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-03-01 10:05 -0700
                                          Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-01 19:29 +0200
                                            Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 04:36 +1100
                                            Re: Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-03-01 11:06 -0700
                                            Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-03-01 13:30 -0500
                                            Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-02 08:35 +0000
                                              Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 11:35 +0200
                                                Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 11:40 +0200
                                                Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-02 21:07 +1100
                                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 12:37 +0200
                                                Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-02 10:44 +0000
                                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 13:33 +0200
                                                    Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-03 01:50 +0000
                                                Re: Can global variable be passed into Python function? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-02 13:04 +0000
                                                Re: Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-03-02 11:48 -0700
                                                  Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-02 23:03 +0200
                                                    Re: Can global variable be passed into Python function? Roy Smith <roy@panix.com> - 2014-03-02 16:16 -0500
                                                    Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-03-03 08:28 +1100
                                                    Re: Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-03-02 14:44 -0700
                                                      Re: Can global variable be passed into Python function? Marko Rauhamaa <marko@pacujo.net> - 2014-03-03 00:46 +0200
                                    Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 17:18 +0000
                            Re: Can global variable be passed into Python function? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-01 00:58 +0000
                    Re: Can global variable be passed into Python function? Michael Torrie <torriem@gmail.com> - 2014-02-28 07:49 -0700
                  Re: Can global variable be passed into Python function? Chris Angelico <rosuav@gmail.com> - 2014-02-28 20:00 +1100
                  Re: Can global variable be passed into Python function? Grant Edwards <invalid@invalid.invalid> - 2014-02-28 14:20 +0000
          References, and avoiding use of “variable” (was: Can global variable be passed into Python function?) Ben Finney <ben+python@benfinney.id.au> - 2014-02-28 13:46 +1100
          Re: References, and avoiding use of ???variable??? (was: Can global variable be passed into Python function?) Neil Cerutti <neilc@norwich.edu> - 2014-02-28 14:30 +0000
          Re: References, and avoiding use of ???variable??? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 10:33 +1100
            Re: References, and avoiding use of ???variable??? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-03-01 16:08 +1300
              Re: References, and avoiding use of ???variable??? Ben Finney <ben+python@benfinney.id.au> - 2014-03-01 15:22 +1100

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#66792 — Can global variable be passed into Python function?

I need to pass a global variable into a python function. However, the global variable does not seem to be assigned after the function ends. Is it because parameters are not passed by reference? How can I get function parameters to be passed by reference in Python?

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#66807

Sam <lightaiyee@gmail.com> writes:

> I need to pass a global variable into a python function.

Python does not really have the concept "variable".

What appears to be a variable is in fact only the binding of an
object to a name. If you assign something to a variable,
all you do is binding a different object to the name.

Thus, if you have:

      i = 1
      def f(x): x = 5

      f(i)

Then "i" will remain "1" and not become "5".
The effect of "x = 5" is that the name "x" gets bound to "5"
(where is formerly was bound to "1").

>However, the global variable does not seem to be assigned after the function ends. Is it because parameters are not passed by reference?

Python lacks the notion of "variable". Thus, it does not
pass variables into functions but objects.
The objects, however, get passed by reference.

>How can I get function parameters to be passed by reference in Python?

You can implement your own concept of variable, e.g. like this:

    class Variable(object):
      def __init__(self, value): self.value = value

The little program above then becomes:

    i = Variable(1)
    def f(x): x.value = 5

    f(i)
    i.value # this is now 5

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#66816

dieter writes:
> Sam writes:
> 
> > I need to pass a global variable into a python function.
> 
> Python does not really have the concept "variable".
> 
> What appears to be a variable is in fact only the binding of an
> object to a name. If you assign something to a variable,
> all you do is binding a different object to the name.
> 
> Thus, if you have:
> 
>       i = 1
>       def f(x): x = 5
> 
>       f(i)
> 
> Then "i" will remain "1" and not become "5".
> The effect of "x = 5" is that the name "x" gets bound to "5"
> (where is formerly was bound to "1").

In alleged contrast, the observable behaviour of languages that "have
variables" is the same. This is not considered confusing by the people
who insist that there are no variables in Python.

Note: I do not object to Python's choice of different preferred
terminology. Python seems to be doing fine with that. I do object to
the insistence that Python needs this different terminology because it
behaves differently from the languages where variables are called
variables. Python behaves the same.

Here's Java, where I demonstrate with both a class variable i and a
local variable j; I used String so that this same demonstration will
still serve after someone points out that Java's primite numbers are
not quite objects, which is true but irrelevant:

$ cat Var.java
public class Var {
    public static String i = "1";
    public static String f(String x) {
        x = "5";
        return x;
    }
    public static void main(String... args) {
        String j = "2";
        System.out.println("i == " + i + ", j == " + j);
        System.out.println("f(i) == " + f(i) + ", " +
                           "f(j) == " + f(j));
        System.out.println("i == " + i + ", j == " + j);
    }
}
$ javac Var.java 
$ java -cp . Var 
i == 1, j == 2
f(i) == 5, f(j) == 5
i == 1, j == 2
$ 

This is C, where I again demonstrate with both a global and a local
variable, but here I leave them as ints; I think C might be a language
where the word "variable" has been used to mean something like a block
of memory, which is a different usage; still, would someone be willing
to explain the behaviour of this program by "C lacks variables":

$ cat var.c
#include <stdio.h>
int i = 1;
int f(int x) { x = 5; return x; }
main() {
  int j = 2;
  printf("i == %d, j == %d\n", i, j);
  printf("f(i) == %d, f(j) == %d\n", f(i), f(j));
  printf("i == %d, j == %d\n", i, j);
}
$ gcc -o var var.c
$ ./var 
i == 1, j == 2
f(i) == 5, f(j) == 5
i == 1, j == 2
$ 

This is Scheme, which is where I come from; its variables behave the
same as the corresponding machinery in Python with regard to the
problem at hand:

$ cat var.scm 
(define i 1)
(define (f x) (set! x 5) x)
(let ((j 2))
  (display "i == ") (write i) (display ", j == ") (write j) (newline)
  (display "f(i) == ") (write (f i))
  (display ", f(j) == ") (write (f j)) (newline)
  (display "i == ") (write i) (display ", j == ") (write j) (newline))
$ gsi var.scm 
i == 1, j == 2
f(i) == 5, f(j) == 5
i == 1, j == 2
$ 

> > However, the global variable does not seem to be assigned after
> > the function ends. Is it because parameters are not passed by
> > reference?
> 
> Python lacks the notion of "variable". Thus, it does not
> pass variables into functions but objects.
> The objects, however, get passed by reference.

I think the relevant answer is simply that i and x are different
variables. In Python terminology, I think you would have to say that
they are different names. With a slight change, you would need to
explain how i and i are different names (I think), and then you would
introduce the concept of different namespaces.

Python indeed does not pass variables (and this is a relevant), but
neither do the other languages that "have variables".

[snip]

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#66822

Jussi Piitulainen <jpiitula@ling.helsinki.fi>:

> In alleged contrast, the observable behaviour of languages that "have
> variables" is the same. This is not considered confusing by the people
> who insist that there are no variables in Python.

But of course there are variables in Python:

   By “frozen” we mean that all local state is retained, including the
   current bindings of local variables, [...] (<URL:
   http://docs.python.org/3.2/reference/simple_stmts.html
   #the-yield-statement>)

   The public names defined by a module are determined by checking the
   module’s namespace for a variable named __all__ (<URL:
   http://docs.python.org/3.2/reference/simple_stmts.html
   #the-import-statement>)

   It would be impossible to assign to a global variable without global
   (<URL: http://docs.python.org/3.2/reference/simple_stmts.html
   #the-global-statement>)

etc etc.

However, your point about "observable behavior" is key, and Python users
of all people should get the principle (as it is related to duck
typing).

> Python indeed does not pass variables (and this is a relevant), but
> neither do the other languages that "have variables".

Maybe the idea comes from the fact that you can't easily pass a
variable to a function for modification.

Consider this C function:

   void make_printable(const char **ref)
   {
       if (!*ref)
           *ref = "<NULL>";
   }

which allows:

   make_printable(&x);
   make_printable(&s->name);
   make_printable(&a[i]);


Marko

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#66808

Sam wrote:

> I need to pass a global variable into a python function. However, the
> global variable does not seem to be assigned after the function ends. Is
> it because parameters are not passed by reference? How can I get function
> parameters to be passed by reference in Python?

If the variable you want to process is always the same global variable you 
can declare it:

>>> x = 0
>>> def inc_x():
...     global x
...     x += 1
... 
>>> x
0
>>> inc_x()
>>> x
1
>>> inc_x(); inc_x()
>>> x
3

If you want to change ("rebind") varying global names you have to be 
explicit:

>>> def inc(x):
...     return x + 1
... 
>>> x = 0
>>> x = inc(x)
>>> y = 0
>>> y = inc(y)
>>> y = inc(y)
>>> x, y
(1, 2)

Then there are ugly hacks that make your code hard to follow. Don't use 
these:

>>> def inc(name):
...     globals()[name] += 1
... 
>>> inc("x")
>>> inc("x")
>>> x
3

>>> def inc(module, name):
...     setattr(module, name, getattr(module, name) + 1)
... 
>>> import __main__
>>> inc(__main__, "x")
>>> inc(__main__, "x")
>>> inc(__main__, "x")
>>> x
6

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#66814

On 02/20/2014 10:37 PM, Sam wrote:
> I need to pass a global variable into a python function. However, the global variable does not seem to be assigned after the function ends. Is it because parameters are not passed by reference? How can I get function parameters to be passed by reference in Python?

Are you passing a value *into* a function, or back *out of* the 
function?  These are two very different things, and your question 
mentions both and seems to confuse them.

You can pass any value into a function through its parameters, whether 
that value comes from a local variable, global variable, or the result 
of some computation. (But consider: it is the value that is being passed 
in -- not the variable that contains that value.) You can't pass values 
back out from a function through assignment to any of the parameters.

The global statement is a way to allow a function to assign to a global 
variable, but this would not be considered "passing" a global into a 
function.  It's just a way to access and assign to a global variable 
from withing a function.

v = 123

def f(...):
    global v  # Now v refers to the global v
    print(v)  # Accesses and prints the global v
    v = 456 # Assigns to the global v.

Gary Herron

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#66815

On Thu, 20 Feb 2014 22:37:59 -0800, Sam wrote:

> I need to pass a global variable into a python function. However, the
> global variable does not seem to be assigned after the function ends. Is
> it because parameters are not passed by reference? How can I get
> function parameters to be passed by reference in Python?

You cannot. Python does not support either pass-by-reference or pass-by-
value calling conventions. Instead, it supports the same calling 
convention as Java, Ruby and other modern languages (which confusingly 
those two languages both call something different), "call by object 
sharing".

To understand more about Python's calling convention, and why neither 
call-by-reference nor call-by-value are appropriate, please read these 
articles:

https://mail.python.org/pipermail/tutor/2010-December/080505.html
http://effbot.org/zone/call-by-object.htm

and also see the Wikipedia article:

http://en.wikipedia.org/wiki/Evaluation_strategy


If you show us a sample of your code, together of a sample of how you 
expect it to work, we can suggest an alternate way to solve that problem.



-- 
Steven

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#66829

On 2/21/14 2:23 AM, dieter wrote:
> Sam<lightaiyee@gmail.com>  writes:
>
>> >I need to pass a global variable into a python function.
> Python does not really have the concept "variable".
>
> What appears to be a variable is in fact only the binding of an
> object to a name. If you assign something to a variable,
> all you do is binding a different object to the name.
>

Man, do I hate this idea that Python has no variables.  It has variables 
(names associated with values, and the values can change over the course 
of the program), they just don't work the same as C or Fortran 
variables. In fact, they work exactly the same as Javascript or Ruby 
variables.

Python's variables are names bound to values.
http://nedbatchelder.com/text/names.html has lots more details.


-- 
Ned Batchelder, http://nedbatchelder.com

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#66830

Ned Batchelder <ned@nedbatchelder.com>:

> Man, do I hate this idea that Python has no variables. It has
> variables (names associated with values, and the values can change
> over the course of the program),

In classic functional programming, the values of variables can't change
but they are still called variables (even though "parameters" might be
more fitting).

> they just don't work the same as C or Fortran variables. In fact, they
> work exactly the same as Javascript or Ruby variables.

Apart from a fact that a C variable has an address (references are
first-class objects, if you will), I really don't see a difference
between a C variable and a Python variable.


Marko

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#66869

On Fri, 21 Feb 2014 07:13:25 -0500, Ned Batchelder wrote:

> On 2/21/14 2:23 AM, dieter wrote:
>> Sam<lightaiyee@gmail.com>  writes:
>>
>>> >I need to pass a global variable into a python function.
>> Python does not really have the concept "variable".
>>
>> What appears to be a variable is in fact only the binding of an object
>> to a name. If you assign something to a variable, all you do is binding
>> a different object to the name.
>>
>>
> Man, do I hate this idea that Python has no variables.  It has variables
> (names associated with values, and the values can change over the course
> of the program), they just don't work the same as C or Fortran
> variables. In fact, they work exactly the same as Javascript or Ruby
> variables.

I sympathise with your view. It seems quite ridiculous to claim that 
Python has no variables. If it has no variables, what on earth does it 
mean when we say "x = 42"?

But the very ridiculousness is what gives it the attention-grabbing power 
that makes it a useful meme. "Python variables don't behave like C 
variables" might be true, but it's also wish-washy and forgettable.

In my own case, I never quite got Python's name binding semantics until I 
was introduced to the "Python has no variables" meme. That got my 
attention long enough to listen to the actual message: my assumptions 
about how variables behave was based on Pascal semantics, and Python 
doesn't quite follow the same rules. Consequently, if I implicitly define 
"variable" to mean "Pascal variables", as I had been, then Python has no 
variables, it has these things called "name bindings".

That's when I got it.

I went through a phase where I too insisted that Python had no variables. 
But then my natural laziness asserted itself, and I decided that the word 
"variable" is too useful to always reject it (and besides, C- and Pascal-
like languages don't have a monopoly on the word "variable"). Now, I use 
the terms "variable" or "reference" or "name binding" as I feel makes the 
most sense in context, depending on my best guess of the risk of 
misunderstanding or confusion.


-- 
Steven

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#66871

On 2/21/14 10:28 PM, Steven D'Aprano wrote:
> On Fri, 21 Feb 2014 07:13:25 -0500, Ned Batchelder wrote:
>
>> On 2/21/14 2:23 AM, dieter wrote:
>>> Sam<lightaiyee@gmail.com>  writes:
>>>
>>>>> I need to pass a global variable into a python function.
>>> Python does not really have the concept "variable".
>>>
>>> What appears to be a variable is in fact only the binding of an object
>>> to a name. If you assign something to a variable, all you do is binding
>>> a different object to the name.
>>>
>>>
>> Man, do I hate this idea that Python has no variables.  It has variables
>> (names associated with values, and the values can change over the course
>> of the program), they just don't work the same as C or Fortran
>> variables. In fact, they work exactly the same as Javascript or Ruby
>> variables.
>
> I sympathise with your view. It seems quite ridiculous to claim that
> Python has no variables. If it has no variables, what on earth does it
> mean when we say "x = 42"?
>
> But the very ridiculousness is what gives it the attention-grabbing power
> that makes it a useful meme. "Python variables don't behave like C
> variables" might be true, but it's also wish-washy and forgettable.
>
> In my own case, I never quite got Python's name binding semantics until I
> was introduced to the "Python has no variables" meme. That got my
> attention long enough to listen to the actual message: my assumptions
> about how variables behave was based on Pascal semantics, and Python
> doesn't quite follow the same rules. Consequently, if I implicitly define
> "variable" to mean "Pascal variables", as I had been, then Python has no
> variables, it has these things called "name bindings".
>
> That's when I got it.
>
> I went through a phase where I too insisted that Python had no variables.
> But then my natural laziness asserted itself, and I decided that the word
> "variable" is too useful to always reject it (and besides, C- and Pascal-
> like languages don't have a monopoly on the word "variable"). Now, I use
> the terms "variable" or "reference" or "name binding" as I feel makes the
> most sense in context, depending on my best guess of the risk of
> misunderstanding or confusion.
>
>

This is an interesting perspective, thanks.

I think it might be that the OP's question, "Can a global variable be 
passed into a function", really had nothing to do with the 
name/value/variable distinction, and we've done it again: taken a simple 
question and spun off into pedantry and trivia.


-- 
Ned Batchelder, http://nedbatchelder.com

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#66875

On Fri, 21 Feb 2014 22:45:14 -0500, Ned Batchelder wrote:

> I think it might be that the OP's question, "Can a global variable be
> passed into a function", really had nothing to do with the
> name/value/variable distinction, and we've done it again: taken a simple
> question and spun off into pedantry and trivia.

You might be right, but the OP's question isn't really clear. Surely he 
didn't mean something as trivial as this?

x = 1  # This is a global
some_function(x)  # Passing a global into a function


His description, especially the comment about pass by reference, suggests 
that there is more to it than just passing a global variable as argument 
to a function. I think he is trying to *write* to the variable as well, 
as an output variable, something like this:

x = 1
y = 2
some_function(x)
assert x == 99
some_function(y)
assert y == 99


Sadly, it appears to have been a drive-by question: Sam tossed a question 
out the window as he drove by, and may never come back for the answer... 
I hope I'm wrong, but it's been nearly 24 hours since the question was 
asked and not a peep from the OP.


Sam, if you're out there reading this, please respond with more detail 
about what you are trying to do!


-- 
Steven

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#66837

On Feb 21, 2014, at 4:13 AM, Ned Batchelder <ned@nedbatchelder.com> wrote:

> Man, do I hate this idea that Python has no variables.  It has variables (names associated with values, and the values can change over the course of the program), they just don't work the same as C or Fortran variables. In fact, they work exactly the same as Javascript or Ruby variables.

Thank you!

+11

I get tired of the “Python doesn’t have variables” line.

What makes Python variables/bindings/references/aliases/namedvalues/slots/bucketsofstuff surprising to new arrivals from other language kingdoms, is that accessing is pragmatically implicit (walks the scope tree for you) and assignment may require explicitness. IOW, for some “variables”, you have to do something explicit to make the variable you want to refer to, vary. Some might say there is a lack of symmetry. Pros and cons.

Personally, I don’t care. It’s one of those lessons you just learn as you go.

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#66839

On Sat, Feb 22, 2014 at 4:59 AM, Travis Griggs <travisgriggs@gmail.com> wrote:
> What makes Python variables/bindings/references/aliases/namedvalues/slots/bucketsofstuff surprising to new arrivals from other language kingdoms, is that accessing is pragmatically implicit (walks the scope tree for you) and assignment may require explicitness. IOW, for some “variables”, you have to do something explicit to make the variable you want to refer to, vary. Some might say there is a lack of symmetry. Pros and cons.
>

What you're looking at there, I think, is actually quite tangential to
the question of Python having/not having variables, and it's to do
with scoping rules. Correct me if I'm wrong.

g = "global"
c = 0
def f():
    print(g) # References two globals
    l = "local"
    print(l) # References one global and one local
    global c
    c = 1 # References one global

As an alternative, Python could have asked us to declare the other way:

def f():
    print(g) # References two globals
    local l
    l = "local"
    print(l) # References one global and one local
    c = 1 # References one global

It would still be the same name binding / object reference model, with
just a different keyword used to change the default behaviour of name
lookups. And the difference is comparatively slight. We get an
encouragement to use locals rather than globals, but on the flip side,
we need two keywords (global/nonlocal) where a single one (local, or
as ECMAScript puts it, "var") could handle the other case. It's a lack
of symmetry, but having worked with PHP (where you have to declare
*every* global, except for the magical superglobals, and except for
functions (which are in a completely different namespace), and except
for constants), I am very much glad that Python puts everything in
together as just "names", and then allows us to reference global names
like "print" without declarations. It's a miswart.

ChrisA

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#66842

On the question of how variables can be passed to functions, C, of
course, has the & operator and Pascal has the "var" keyword.

An analogous thing can be achieved in Python 3 (but not in Python 2, I'm
afraid). The & operator corresponds to an ad hoc property class as in
the program below (not intended to be serious).

The program demonstrates how to write a universal "swap" function that
interchanges two references.


Marko

==clip=clip=clip========================================================
#!/usr/bin/env python3

import sys

def main():
    some_list = [ 'a', 'b', 'c' ]
    some_dict = { 'few' : 'ding',
                  'good' : 'dang',
                  'men' : 'dong' }
    some_value = 'certainly'

    class SomeListElementProperty:
        """&some_list[1]"""
        def get(self):
            return some_list[1]
        def set(self, value):
            some_list[1] = value

    class SomeDictEntryProperty:
        """&some_dict["men"]"""
        def get(self):
            return some_dict['men']
        def set(self, value):
            some_dict['men'] = value

    class SomeValueProperty:
        """&some_value"""
        def get(self):
            return some_value
        def set(self, value):
            nonlocal some_value
            some_value = value

    swap(SomeListElementProperty(), SomeDictEntryProperty())
    swap(SomeListElementProperty(), SomeValueProperty())

    sys.stdout.write("{}\n".format(some_list))
    sys.stdout.write("{}\n".format(some_dict))
    sys.stdout.write("{}\n".format(some_value))

def swap(px, py):
    x = px.get()
    y = py.get()
    px.set(y)
    py.set(x)

if __name__ == '__main__':
    main()
==clip=clip=clip========================================================

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#66876

On Sat, Feb 22, 2014 at 6:20 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
> On the question of how variables can be passed to functions, C, of
> course, has the & operator and Pascal has the "var" keyword.

That doesn't pass a variable into a function, though. It passes the
address of that variable, and C lets you stuff something into an
address. That's not the same thing.

ChrisA

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#66878

On Sat, 22 Feb 2014 17:36:52 +1100, Chris Angelico wrote:

> On Sat, Feb 22, 2014 at 6:20 AM, Marko Rauhamaa <marko@pacujo.net>
> wrote:
>> On the question of how variables can be passed to functions, C, of
>> course, has the & operator and Pascal has the "var" keyword.
> 
> That doesn't pass a variable into a function, though. It passes the
> address of that variable, and C lets you stuff something into an
> address. That's not the same thing.

Be careful about conflating the implementation with the interface. As I 
understand it, the interface C literally is that &x gives you the address 
of x. But that's not what the var keyword is for in Pascal (although that 
may be how it is implemented).

In Pascal, if you have a function or procedure:

procedure plus(a:integer, var b:integer);
  begin
    b := a+b;
  end;


and a couple of variables in some other scope, for simplicity lets make 
them global:

var
  foo: int;
  bar: int;

begin
  foo := 23;
  bar := 1;
  plus(bar, foo);
  writeln(foo);
end.

the output will be 24. If we could peek into procedure plus, we would see 
that argument a was a *copy* of global bar, while argument b wasn't 
merely a copy of foo, it actually was foo. So assigning to b inside plus 
is the same as assigning to foo in the global scope.

If we added a call:

    plus(2, bar);

to the main program, then inside plus argument a would have the value 2, 
and argument b would now be precisely the same variable as global bar. 
After the procedure returns, bar would have the value 3.

Now I daresay that under the hood, Pascal is passing the address of foo 
(or bar) to the procedure plus, but inside plus you don't see that 
address as the value of b. You see the value of foo (or bar).

C does not do that -- you have to manually manage the pointers yourself, 
while Pascal does it for you. And Python also has nothing like that.



-- 
Steven

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#66880

On Sat, Feb 22, 2014 at 6:18 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Now I daresay that under the hood, Pascal is passing the address of foo
> (or bar) to the procedure plus, but inside plus you don't see that
> address as the value of b. You see the value of foo (or bar).
>
> C does not do that -- you have to manually manage the pointers yourself,
> while Pascal does it for you. And Python also has nothing like that.

Yep. I should have clarified that I wasn't talking about Pascal; I'm
not fluent in the language (last time I did anything at all with
Pascal was probably about ten years ago, and not much then). In C, it
strictly does what I said: & takes the address of something, *
dereferences an address. There's no way to "pass a variable" - you
have to pass the address, and that has consequences if, for instance,
you *return* an address and the variable ceases to exist. (Does Pascal
have an equivalent of that?)

And Python has no such concept, anywhere. But anything that you can
achieve in C using pointers, you can probably achieve in Python using
more complex objects.

ChrisA

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#66881

>>> # a swapping variant
>>> def swap(a, b):
...     ab = [a, b]
...     ab[1], ab[0] = ab[0], ab[1]
...     return ab[0], ab[1]
...     
>>> a = 111
>>> id(a)
505627864
>>> b = 999
>>> id(b)
58278640
>>> a, b = swap(a, b)
>>> a, id(a)
(999, 58278640)
>>> b, id(b)
(111, 505627864)

jmf

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#66882

On Sat, Feb 22, 2014 at 7:02 PM,  <wxjmfauth@gmail.com> wrote:
>>>> # a swapping variant
>>>> def swap(a, b):
> ...     ab = [a, b]
> ...     ab[1], ab[0] = ab[0], ab[1]
> ...     return ab[0], ab[1]

Provably identical to:

def swap(a, b):
    return b, a

The rest is just fluff.

ChrisA

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