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Re: Python Newbie

References <cad0eacc-6040-4a00-bd05-7fabfd2fa70e@googlegroups.com> <5c262e95-b3a8-4f2a-b752-84b30bf4f81e@googlegroups.com>
Date 2013-02-22 10:21 +1100
Subject Re: Python Newbie
From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.2213.1361488895.2939.python-list@python.org> (permalink)

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On Fri, Feb 22, 2013 at 9:40 AM,  <piterrr.dolinski@gmail.com> wrote:
> Thanks to all for quick relies.
>
> Chris, you are (almost) spot on with the if blocks indentation. This is what I do, and it has served me well for 15 years.
>
> code
> code
>
>    if (some condition)
>    {
>       code
>       code
>    }
>

I understand you have the freedom to do that in most languages, but
that's simply a restriction of Python: you have to use a more
conventional indentation system. Personally, I don't see the 'if' as
being special here, and the body of it (which IS special, as it may or
may not be executed) is already standing out.

> I am nervous about using variables "out of the blue", without having to declare them. For example, when I write "i = 0" it is perfectly OK to Python without 'i' being declared earlier. How do I know that I haven't used this variable earlier and I am unintentionally overwriting the value? I find I constantly have to use the search facility in the editor, which is not fun.
>
> You see, Javascript, for one, behaves the same way as Python (no variable declaration) but JS has curly braces and you know the variable you have just used is limited in scope to the code within the { }. With Python, you have to search the whole file.

That's a fair point. The elision of variable declarations is a design
decision that Python is unlikely to reverse, and it happens to be one
I disagree with. But it's there, so when I code Python, I accept it :)
There are other languages similar to Python that have strict variable
declarations, and with them the awesomeness that is infinitely nested
scopes; Python just has global (module) scope and function scope, plus
'nonlocal' which can solve some problems (but I've yet to find it do
so without damaging code clarity).

> What about Python's ambiguity?
> For example, in C you would write
>
> if (myVar != 0)
>   do something
>
> in Python, this is legal
>
> if (not myVar):
>   do something
>
> What does this mean? Is it a test for myVar being equal to zero or a test for null, or else?

Python has a state called "truthiness". Generally speaking, something
with content is true, and something without content is false. The None
singleton, empty lists, empty tuples, the integer 0, and a regular
expression result that didn't match, all evaluate as False in a
boolean context; most other things evaluate as True. If you
specifically care if it's not zero, you ask if it's not zero; if you
want to know if it's falsy, you check "not X". The facilities are
there to do whatever you want.

ChrisA

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Thread

Python Newbie Piterrr <piterrr.dolinski@gmail.com> - 2013-02-21 13:26 -0800
  Re: Python Newbie Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-21 14:54 -0700
  Re: Python Newbie MRAB <python@mrabarnett.plus.com> - 2013-02-21 21:58 +0000
  Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-22 08:59 +1100
  Re: Python Newbie Peter Pearson <ppearson@nowhere.invalid> - 2013-02-21 22:03 +0000
  Re: Python Newbie Dave Angel <davea@davea.name> - 2013-02-21 17:22 -0500
  Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-21 14:40 -0800
    Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-22 10:21 +1100
      Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-21 15:34 -0800
        Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-21 23:48 +0000
        Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-22 11:32 +1100
        Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 11:58 -0700
      Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-21 15:34 -0800
    Re: Python Newbie Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-21 23:27 +0000
    Re: Python Newbie Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-21 16:55 -0700
    Re: Python Newbie rusi <rustompmody@gmail.com> - 2013-02-21 22:57 -0800
    Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-22 10:26 +0000
      Re: Python Newbie Steve Simmons <square.steve@gmail.com> - 2013-02-22 12:05 +0100
      Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-22 22:23 +1100
    Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 16:04 -0700
    Re: Python Newbie Vito De Tullio <vito.detullio@gmail.com> - 2013-02-24 09:23 +0100
    Re: Python Newbie "J.R." <groups_jr-1@yahoo.com.br> - 2013-02-24 23:02 -0300
      Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 21:03 -0500
        Re: Python Newbie "J.R." <groups_jr-1@yahoo.com.br> - 2013-02-24 23:35 -0300
        Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 13:31 +1100
  Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-21 19:35 -0500
  Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-21 23:50 -0500
    Re: Python Newbie Rui Maciel <rui.maciel@gmail.com> - 2013-02-22 11:58 +0000
      Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-22 23:12 +1100
        Re: Python Newbie Rui Maciel <rui.maciel@gmail.com> - 2013-02-22 13:50 +0000
          Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 01:05 +1100
            Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-23 00:03 +0000
              Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 11:21 +1100
          Re: Python Newbie Duncan Booth <duncan.booth@invalid.invalid> - 2013-02-22 14:26 +0000
            Re: Python Newbie Steve Simmons <square.steve@gmail.com> - 2013-02-22 15:45 +0100
              Re: Python Newbie Duncan Booth <duncan.booth@invalid.invalid> - 2013-02-22 15:02 +0000
            Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 02:06 +1100
              Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-22 13:37 -0800
                Re: Python Newbie Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-22 22:08 +0000
                Re: Python Newbie Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-22 15:45 -0700
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-22 15:38 -0800
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 11:17 +1100
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-23 13:29 -0500
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-24 08:38 +1100
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 15:52 -0700
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-24 10:18 +1100
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-23 15:46 -0800
                Re: Python Newbie Larry Hudson <orgnut@yahoo.com> - 2013-02-23 20:20 -0800
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-24 14:34 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 07:46 -0800
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 02:52 +1100
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 11:22 -0500
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-24 17:44 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 11:29 -0800
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-24 21:35 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 14:43 -0800
                Re: Python Newbie Joel Goldstick <joel.goldstick@gmail.com> - 2013-02-24 18:05 -0500
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-24 23:13 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 14:43 -0800
                Re: Python Newbie Larry Hudson <orgnut@yahoo.com> - 2013-02-26 00:32 -0800
                Re: Python Newbie rurpy@yahoo.com - 2013-02-26 10:23 -0800
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-26 10:59 -0800
                Re: Python Newbie rurpy@yahoo.com - 2013-02-26 13:30 -0800
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-24 18:31 -0700
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 09:08 +1100
                Re: Python Newbie Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-24 23:18 +0000
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-24 22:51 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 15:38 -0800
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 10:45 +1100
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-24 15:53 -0800
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 16:08 -0800
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-25 00:28 +0000
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-25 00:38 +0000
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-24 16:33 -0800
                Re: Python Newbie Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-25 00:45 +0000
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 19:50 -0500
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-25 01:04 +0000
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 12:27 +1100
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-24 18:42 -0700
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 12:24 +1100
                Re: Python Newbie Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-25 01:44 +0000
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 12:53 +1100
                Re: Python Newbie MRAB <python@mrabarnett.plus.com> - 2013-02-25 02:23 +0000
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-24 18:59 -0800
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 16:08 -0800
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 19:42 -0500
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 15:38 -0800
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-24 23:21 +0000
                Re: Python Newbie Dave Angel <davea@davea.name> - 2013-02-24 17:47 -0500
                Re: Python Newbie Serhiy Storchaka <storchaka@gmail.com> - 2013-02-25 14:40 +0200
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 07:46 -0800
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 22:23 -0700
                Re: Python Newbie MRAB <python@mrabarnett.plus.com> - 2013-02-24 00:11 +0000
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-24 12:37 -0500
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-24 10:56 -0700
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 13:07 -0500
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-24 21:01 -0500
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-22 15:38 -0800
                Re: Python Newbie Terry Reedy <tjreedy@udel.edu> - 2013-02-22 20:04 -0500
                Re: Python Newbie rurpy@yahoo.com - 2013-02-22 18:48 -0800
                Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-22 20:47 -0500
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-23 02:02 +0000
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 13:18 +1100
                Re: Python Newbie Grant Edwards <invalid@invalid.invalid> - 2013-02-24 18:19 +0000
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 07:25 +1100
                Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-22 21:40 -0500
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-23 13:48 +1100
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-23 02:59 +0000
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-23 13:34 -0500
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-24 08:40 +1100
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-24 12:41 -0500
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-23 04:13 +0000
                Re: Python Newbie Serhiy Storchaka <storchaka@gmail.com> - 2013-02-23 11:48 +0200
                Re: Python Newbie Rui Maciel <rui.maciel@gmail.com> - 2013-02-23 12:30 +0000
                Re: Python Newbie Steve Simmons <square.steve@gmail.com> - 2013-02-23 16:43 +0100
                Re: Python Newbie jmfauth <wxjmfauth@gmail.com> - 2013-02-23 10:44 -0800
                Re: Python Newbie Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-23 12:13 -0700
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-23 11:08 -0800
                Re: Python Newbie jmfauth <wxjmfauth@gmail.com> - 2013-02-23 12:53 -0800
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-24 08:48 +1100
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-24 00:02 +0000
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 12:16 -0700
                Re: Python Newbie Matej Cepl <mcepl@redhat.com> - 2013-02-24 00:06 +0100
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-24 02:51 +1100
                Re: Python Newbie Matej Cepl <mcepl@redhat.com> - 2013-02-24 00:04 +0100
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-23 08:32 -0800
                Re: Python Newbie Steve Simmons <square.steve@gmail.com> - 2013-02-23 18:39 +0100
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 12:19 -0700
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-24 17:11 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 11:40 -0800
                Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-24 15:06 -0500
                Re: Python Newbie "Michael Ross" <gmx@ross.cx> - 2013-02-24 21:33 +0100
                Re: Python Newbie MRAB <python@mrabarnett.plus.com> - 2013-02-24 20:34 +0000
                Re: Python Newbie Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-24 20:41 +0000
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-24 12:34 -0800
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 07:42 +1100
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 15:48 -0500
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-24 21:58 +0000
                Re: Python Newbie Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-24 21:08 -0500
                Re: Python Newbie Joshua Landau <joshua.landau.ws@gmail.com> - 2013-02-25 02:59 +0000
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 07:47 +1100
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 07:58 +1100
                Re: Python Newbie Roy Smith <roy@panix.com> - 2013-02-24 16:08 -0500
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 08:44 +1100
                Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-24 17:40 -0500
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-25 01:11 +0000
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-25 00:42 +0000
                Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-24 18:34 -0700
                Re: Python Newbie Ethan Furman <ethan@stoneleaf.us> - 2013-02-24 14:33 -0800
                Re: Python Newbie Albert Hopkins <marduk@letterboxes.org> - 2013-02-24 18:32 -0500
                Re: Python Newbie Chris Angelico <rosuav@gmail.com> - 2013-02-25 10:44 +1100
                Re: Python Newbie Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-25 01:06 +0000
                Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-24 11:40 -0800
              Re: Python Newbie piterrr.dolinski@gmail.com - 2013-02-22 13:37 -0800
      Re: Python Newbie Mitya Sirenef <msirenef@lightbird.net> - 2013-02-22 20:05 -0500
  Re: Python Newbie Gene Heskett <gheskett@wdtv.com> - 2013-02-23 12:32 -0500
  Re: Python Newbie Steve Simmons <square.steve@gmail.com> - 2013-02-23 19:10 +0100
  Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 11:40 -0700
  Re: Python Newbie Michael Torrie <torriem@gmail.com> - 2013-02-23 12:15 -0700
  Re: Python Newbie Gene Heskett <gheskett@wdtv.com> - 2013-02-23 17:49 -0500
  Re: Python Newbie Nick Mellor <thebalancepro@gmail.com> - 2013-02-25 19:37 -0800

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