[Tutor] Noob: nested if-clauses

[STF]

Thanks to Joel and Alan for replying.

On 24 January 2016 at 22:08, Alan Gauld <alan.gauld at btinternet.com> 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.