Re: [Tutor] Noob: nested if-clauses

[Alan Gauld]

On 30/01/16 01:06, Alan Gauld wrote:

> or CD to the folder:
> 
> C:\SOME\PATH> CD  D:\mycode\abc
> D:
> D:\mycode\abc>

Oops, that sequence should be:

C:\SOME\PATH> CD  D:\mycode\abc
C:\SOME\PATH> D:
D:\mycode\abc>

sorry about that.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] Noob: nested if-clauses

[Alan Gauld]

On 29/01/16 17:41, STF wrote:

> what that gives.  IDLE is indeed easier to use than the "DOS-style" Python
> command-line window.  

One thing I'd say is that you can tweak the DOS CMD window quite
a lot to make it better for IDLE(and other interpreters). But
IDLE is probably still better for most folks.

> How do you call this thing, BTW?  I'm unable to
> understand how to navigate inside this thing.  

I'm not totally clear what you mean here.
You start IDLE from the start menu or desktop shortcut.
That gets you to the interactive shell which is a version
of the python interpreter running inside idle

> I mean, when I open it, in which folder am I in?

You can find out with

>>> import os
>>> print ( os.getcwd() )

But its rarely important because you normally use
File->Open to open a file, or File->New to create a new
one and save it wherever you want).

Once you do that IDLE opens a new editor (as opposed
to shell) window. From there you can use the Run menu
to execute your code with the output appearing in the
original shell window.

> Suppose I have a Python file in
> D:\mycode\abc\myfile.py.  How to run it?

Within IDLE use File->Open to locate and load it.
Then use the Run->Riun Module menu command (shortcut F5)

Outside idle use

C:\SOME\PATH> python D:\mycode\abc\myfile.py

You can of course create a shortcut to do that.

or CD to the folder:

C:\SOME\PATH> CD  D:\mycode\abc
D:
D:\mycode\abc>

then type

D:\mycode\abc> python myfile.py

hth
-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] Noob: nested if-clauses

[John Wong]

On Fri, Jan 29, 2016 at 3:13 PM, Alan Gauld 
wrote:

>
> When I first heard that python was white-space sensitive I
> thought, oh no! But now I see it as a huge strength of the
> language. Once you get used to it you will find it helps
> far more than it hinders - just avoid tabs and/or map your
> tab key to spaces.
>
>
Just want to emphasize: use a tool that actually works for you and for the
programming tool. In general, any modern IDE is capable of doing the right
thing. NotePad++ is also capable, but avoid anything like WordPad or
NotePad, if they are still around...
Lastly, most projects I encounter do use 4-space, but some projects (and
notably Google projects internally) would use 2-space, so you almost never
have to worry about mixing 4-space and 2-space in your code. It just happen
that sometimes some people publish code under tab or 2 space and if you
just copy-paste you can run into issues, just FYI for the beginners.

Thanks.

John
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Re: [Tutor] Noob: nested if-clauses

[STF]

On 25 January 2016 at 21:46, Alan Gauld  wrote:

> On 25/01/16 15:52, STF wrote:
>
> > It's a total fluke.  I put the indentation like this to *visually* help
> > myself understand what I was going to write.
>
> That's one of the good things about Python, if it looks right
> it very often is right.
>

Actually, in the original example code I type on notepad, I was using
tabs.  But since I can't press Tab inside Gmail interface, I pressed spaces
instead.

My incomprehension is partially due to this YouTube video:
https://youtu.be/W1zOj2CI-KQ (@ 7:00) in which the author didn't insist on
"consistency".

Another reason is that, while tab is interpreted as 4 white spaces in
convention, it's shown as 8 white spaces in Notepad.  So when I opened some
source code, I have different numbers of leading white spaces, which lead
to my confusion.

Personally, I don't find this as a "good thing".  It rather recalls the
horrible dreams I have had when I was using Fortran!  In Fortran, we have
to deal with position of first characters to make things work.  IMO, making
a visual format an essential thing in programming is a very bad idea, if
it's not superficial.



> > In the Python tutorial that I was using, the author only told us to use
> > indentation, without emphasizing on the size of it.
>
> Quite right the amount is not important(syntactically at least) provided
> you are consistent.
>
> > As I'm a newbie, I'm mostly using Python IDLE but sometimes I would use
> > Programmer's Notepad.
>
> I don't know PN but IDLE will keep you right most of the time.
>
> > Let me ask an alternative question.  Suppose I have something like this:
> > 
> >
> > if condition_C:
> > instruction_10
> >instruction_11
> >  instruction_12
> > 
> > There are 4 spaces in front of instruction_10, 3 spaces in front of
> > instruction_11 and 5 spaces in front of instruction_12.
> >
> > What would happen to instruction_11 and instruction_12?
>
> One of the best things about Python is the interpreter.
> Just try it and see. It's much faster than posting a question
> here and you can be sure it's the correct answer! If you
> don't understand what you see, then come here.
>
> Just use some print statements or simple assignments
> for example:
>
> >>> if True:
> ...print 'in the if'
> ...   print 'still here'
> ...  y = 5 * 6
> ...
>
> what happens?
>

OK, I have just tried it (instead of just reading source codes) and I see
what that gives.  IDLE is indeed easier to use than the "DOS-style" Python
command-line window.  How do you call this thing, BTW?  I'm unable to
understand how to navigate inside this thing.  I mean, when I open it, in
which folder am I in?  Suppose I have a Python file in
D:\mycode\abc\myfile.py.  How to run it?

Thx
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Re: [Tutor] Noob: nested if-clauses

[boB Stepp]

On Fri, Jan 29, 2016 at 11:41 AM, STF  wrote:

> ...How do you call this thing, BTW?  I'm unable to
> understand how to navigate inside this thing.  I mean, when I open it, in
> which folder am I in?  Suppose I have a Python file in
> D:\mycode\abc\myfile.py.  How to run it?

IDLE presents itself in two ways.  Normally it defaults to opening up
as the Python interpreter where you see the ">>>" and can type in code
interactively.

Its other view can be accessed by going to the "File" menu and either
choosing "Open..." and browsing to the file you wish to open, such as
"D:\mycode\abc\myfile.py" you mention above, or by creating a new file
with the menu option "New File".  This will open a second window which
is an editor window that you can type in and edit Python code, such as
you were doing in Programmer's Notepad.  To run the code you have
either opened using "Open..." or that you have typed in, use the menu
"Run" and select "Run Module".

Having both of these windows open at the same time is quite handy!  As
you type code into the Editor, you may get stuck and not be sure as to
what you want to do next.  You can then go to the Interpreter window
and type in code snippets, exploring Python's behavior for the code
you are contemplating.  Once you are satisfied, back to the Editor and
enter your code.  Of course you can copy and paste between the two as
well.

Notice that the menu bar has differences between the two windows.  You
should explore the various menu options to see what you can do with
both forms of IDLE.  Don't forget to check out "Help > IDLE Help" for
more information on IDLE's options.  Also note that you can get to the
local Python language docs through "Help > Python Docs".

One more thing to note:  IDLE has shortcut keys.  As you explore the
menus you will see some of them listed next to the menu entries.  For
more go to "Options > Configure IDLE" and you will see a small tabbed
window.  If you go to the "Keys" tab, you can see (and edit) the key
bindings IDLE uses as well as available pre-configured key binding
styles.

Hopefully I'm answering the question(s) you are really asking and have
not gone off on a tangent!


-- 
boB
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Re: [Tutor] Noob: nested if-clauses

[Alan Gauld]

On 29/01/16 17:41, STF wrote:

> Personally, I don't find this as a "good thing".  It rather recalls the
> horrible dreams I have had when I was using Fortran!  In Fortran, we have
> to deal with position of first characters to make things work.  IMO, making
> a visual format an essential thing in programming is a very bad idea, if
> it's not superficial.

I've never done Fortran but I did do COBOL which similarly is fussy
about spacing. But trust me, Python is much more flexible and friendly
in its  use of whitespace. It essentially just asks you to do what
you should be doing anyways.

And the way it works avoids most of the dangling else errors
you get in languages like C/Java etc (And I had >10 years
experience with those before discovering python.)

When I first heard that python was white-space sensitive I
thought, oh no! But now I see it as a huge strength of the
language. Once you get used to it you will find it helps
far more than it hinders - just avoid tabs and/or map your
tab key to spaces.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] Noob: nested if-clauses

[STF]

Thanks to Joel and Alan for replying.

On 24 January 2016 at 22:08, Alan Gauld  wrote:

> On 24/01/16 19:42, STF wrote:
>
> > Let's see the following instructions:
> > 
> > if condition_A:
> > instruction_1
> > instruction_2
> > if condition_B:
> >   instruction_3
> >   instruction_4
> > instruction_5
> > else:
> > instruction_6
> > 
> >
> > * How to make Pythom understand that instruction_4 is a part of
> condition_B
> > if-clause but not a direct instruction of condition_A if-clause?
>
> You've done it above by the indentation.
>

It's a total fluke.  I put the indentation like this to *visually* help
myself understand what I was going to write.

In the Python tutorial that I was using, the author only told us to use
indentation, without emphasizing on the size of it.


> > to make Python understand that instruction_5 is outside of condition_B
> > if-clause?  Just by the number of white spaces in front of every
> > instruction??
>
> Yes, the indent level tells Python where the instruction should be.
>
> > * How to make Python understand that "else" belongs to the first
> > condition_A if-clause, not to the immediate condition_B if-clause?
>
> Again you've done it already, just use the indent level.
>
> > * Suppose I put four white spaces in front of instruction_1, and then
> "tab
> > key" in front of instruction_2, would this break things?
>
> In Python 2 things are a wee bit flexible but in Python 3 less so.
> But in general avoid mixing them, stick to spaces. Most Python
> programmers set their text editor/IDE to convert tabs to
> spaces(usually 4)
>
> > most intelligent text editors would insert automatically a tab in place
> of
> > 4 white spaces after we press Enter on a line with 4 leading white
> spaces.
>
> Most can also be configured not to use tabs at all and
> for Python that's better. Tell us your editor and somebody
> can probably advise on optimum settings.
>

As I'm a newbie, I'm mostly using Python IDLE but sometimes I would use
Programmer's Notepad.


>
> > * Do I really need to keep the consistency of 4 white spaces?  Not one
> more
> > or one less?
>
> No you can have as many or as few as you like in your own code,
> just be consistent. 4 just happens to be esy to read. And its
> the standard for library code so if you want to write some code
> for the standard library you will need to use 4 spaces. In
> the interpreter (>>>) I often only use 2 just to save typing.
> But for production code I stick with 4 - not a problem since
> the editor(vim) does most of the work for me.
>

Let me ask an alternative question.  Suppose I have something like this:


if condition_C:
instruction_10
   instruction_11
 instruction_12

There are 4 spaces in front of instruction_10, 3 spaces in front of
instruction_11 and 5 spaces in front of instruction_12.

What would happen to instruction_11 and instruction_12?  Would Python
ignore them?  Or would they be considered instructions outside the
if-clause?

Thanks again.
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Re: [Tutor] Noob: nested if-clauses

[Danny Yoo]

> if condition_C:
> instruction_10
>instruction_11
>  instruction_12
> 
> There are 4 spaces in front of instruction_10, 3 spaces in front of
> instruction_11 and 5 spaces in front of instruction_12.
>
> What would happen to instruction_11 and instruction_12?  Would Python
> ignore them?  Or would they be considered instructions outside the
> if-clause?
>

You should get an error at program parse time, as the system keeps track of
the indentation used to begin new blocks.  If it sees an indent level that
is inconsistent with those beginnings, it should know to signal a parse
error.

Please feel free to ask questions.  Good luck!

> Thanks again.
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Re: [Tutor] Noob: nested if-clauses

[Alan Gauld]

On 25/01/16 15:52, STF wrote:

> It's a total fluke.  I put the indentation like this to *visually* help
> myself understand what I was going to write.

That's one of the good things about Python, if it looks right
it very often is right.

> In the Python tutorial that I was using, the author only told us to use
> indentation, without emphasizing on the size of it.

Quite right the amount is not important(syntactically at least) provided
you are consistent.

> As I'm a newbie, I'm mostly using Python IDLE but sometimes I would use
> Programmer's Notepad.

I don't know PN but IDLE will keep you right most of the time.

> Let me ask an alternative question.  Suppose I have something like this:
> 
> 
> if condition_C:
> instruction_10
>instruction_11
>  instruction_12
> 
> There are 4 spaces in front of instruction_10, 3 spaces in front of
> instruction_11 and 5 spaces in front of instruction_12.
> 
> What would happen to instruction_11 and instruction_12?  

One of the best things about Python is the interpreter.
Just try it and see. It's much faster than posting a question
here and you can be sure it's the correct answer! If you
don't understand what you see, then come here.

Just use some print statements or simple assignments
for example:

>>> if True:
...print 'in the if'
...   print 'still here'
...  y = 5 * 6
...

what happens?

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] Noob: nested if-clauses

[Alan Gauld]

On 24/01/16 19:42, STF wrote:

> Let's see the following instructions:
> 
> if condition_A:
> instruction_1
> instruction_2
> if condition_B:
>   instruction_3
>   instruction_4
> instruction_5
> else:
> instruction_6
> 
> 
> * How to make Pythom understand that instruction_4 is a part of condition_B
> if-clause but not a direct instruction of condition_A if-clause?  

You've done it above by the indentation.

> to make Python understand that instruction_5 is outside of condition_B
> if-clause?  Just by the number of white spaces in front of every
> instruction??

Yes, the indent level tells Python where the instruction should be.

> * How to make Python understand that "else" belongs to the first
> condition_A if-clause, not to the immediate condition_B if-clause?

Again you've done it already, just use the indent level.

> * Suppose I put four white spaces in front of instruction_1, and then "tab
> key" in front of instruction_2, would this break things?  

In Python 2 things are a wee bit flexible but in Python 3 less so.
But in general avoid mixing them, stick to spaces. Most Python
programmers set their text editor/IDE to convert tabs to
spaces(usually 4)

> most intelligent text editors would insert automatically a tab in place of
> 4 white spaces after we press Enter on a line with 4 leading white spaces.

Most can also be configured not to use tabs at all and
for Python that's better. Tell us your editor and somebody
can probably advise on optimum settings.

> * Do I really need to keep the consistency of 4 white spaces?  Not one more
> or one less?

No you can have as many or as few as you like in your own code,
just be consistent. 4 just happens to be esy to read. And its
the standard for library code so if you want to write some code
for the standard library you will need to use 4 spaces. In
the interpreter (>>>) I often only use 2 just to save typing.
But for production code I stick with 4 - not a problem since
the editor(vim) does most of the work for me.


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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[Tutor] Noob: nested if-clauses

[STF]

Hi,

I've just started to learn Python thru some online courses and websites.
They just teach very basic things.  I've got some questions about "if" that
I'm unable to find the answers.  So let me ask the newbie questions here.

Let's see the following instructions:

if condition_A:
instruction_1
instruction_2
if condition_B:
  instruction_3
  instruction_4
instruction_5
else:
instruction_6


* How to make Pythom understand that instruction_4 is a part of condition_B
if-clause but not a direct instruction of condition_A if-clause?  And how
to make Python understand that instruction_5 is outside of condition_B
if-clause?  Just by the number of white spaces in front of every
instruction??

* How to make Python understand that "else" belongs to the first
condition_A if-clause, not to the immediate condition_B if-clause?

* Suppose I put four white spaces in front of instruction_1, and then "tab
key" in front of instruction_2, would this break things?  I ask so because
most intelligent text editors would insert automatically a tab in place of
4 white spaces after we press Enter on a line with 4 leading white spaces.

* Do I really need to keep the consistency of 4 white spaces?  Not one more
or one less?

Thanks in advance.
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Re: [Tutor] Noob: nested if-clauses

[Joel Goldstick]

On Sun, Jan 24, 2016 at 2:42 PM, STF  wrote:

> Hi,
>
> I've just started to learn Python thru some online courses and websites.
> They just teach very basic things.  I've got some questions about "if" that
> I'm unable to find the answers.  So let me ask the newbie questions here.
>
> Let's see the following instructions:
> 
> if condition_A:
> instruction_1
> instruction_2
> if condition_B:
>   instruction_3
>   instruction_4
> instruction_5
> else:
> instruction_6
> 
>
> * How to make Pythom understand that instruction_4 is a part of condition_B
> if-clause but not a direct instruction of condition_A if-clause?  And how
> to make Python understand that instruction_5 is outside of condition_B
> if-clause?  Just by the number of white spaces in front of every
> instruction??
>
> * How to make Python understand that "else" belongs to the first
> condition_A if-clause, not to the immediate condition_B if-clause?
>
> * Suppose I put four white spaces in front of instruction_1, and then "tab
> key" in front of instruction_2, would this break things?  I ask so because
> most intelligent text editors would insert automatically a tab in place of
> 4 white spaces after we press Enter on a line with 4 leading white spaces.
>
> * Do I really need to keep the consistency of 4 white spaces?  Not one more
> or one less?
>

yes.  you can use 1 or 2 or any number of spaces, but do spacing
consistently.  4 is recommended. Don't mix tabs and spaces

>
> Thanks in advance.
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-- 
Joel Goldstick
http://joelgoldstick.com/stats/birthdays
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