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Re: notebooks default context

  • To: mathgroup at
  • Subject: [mg112311] Re: notebooks default context
  • From: magma <maderri2 at>
  • Date: Thu, 9 Sep 2010 04:21:20 -0400 (EDT)
  • References: <i64kfg$39a$> <i652tt$9sb$>

On Sep 7, 12:07 pm, Albert Retey <a... at> wrote:
> Hi,
> > Firstly a problem, my packages (.m)  keep having their context reset
> > to global every time I open them to edit rather than "unique to each
> > cell"  to which I have previously set them to.
> > THIS IS THE QUESTION (rest waffle)
> > I would like to set a notebooks default context to "Unique to each
> > cell" in a notebook initialisation cell. Usually I use "Unique to this
> > notebook" from the menu (which is fine and persists), however on
> > occasion I would like to tighten things up.
> > ------------
> > ------------
> > I think I don't clearly understand the use of the Package` context
> > instructions. My basic package setup is as follows (which works):
> > BeginPackage[ "Package`"]
> >   Begin[ "Public`"]
> >      preProcess`outNB[nb_] = "something";
> >   End[];
> >   Begin[ "Private`"]
> >   End[]
> > End[]
> > so this is could be one source  of the problem.
> > This is part of a general question on good programming technique in
> > mathematica. My instinct is that for non-trivial notebooks and
> > packages "unique to cell" is the best method and the results should
> > then be put into a context for the notebook to make them available to
> > other cells.
> I think as long as your work is all in one notebook, you usually don't
> really need to take too much care about namespaces (Contexts) at all.
> The use of Contexts only makes sense if your code gets complex enough so
> that the use of different namespaces for different encapsulated parts of
> your code is necessary to keep it maintainable. In these cases I think
> the "best practice" is to create a single file for each of these parts,
> and create a package file (*.m) which contains the BeginPackage/Begin
> stuff that controls in which Context the various symbols will be created.
> You would then use Needs or Get in the notebook(s) that make use of the
> packages. The use of the settings for default contexts is actually a
> relatively new feature that seems to be used mainly in the documentation
> notebooks. It could probably be used also when developing and debugging
> packages or when creating graphical user interfaces, but I don't think
> that there are many people actually using it, and it is not really
> necessary and certainly an advanced feature. I would suggest that you
> don't care about it until you really are sure you know how to use
> contexts and packages in a more standard way.
> Concerning your package structure: you are using a Begin["Public`"]
> which is very unusual, do you have a good reason to do so? The usual
> setup is:
> BeginPackage["MyPackage`"]
>    publicfunction::usage = "publicfunction...";
>    Begin["`Private`"]
>       publicfunction[x_,y_]:=privatefunction[x]+y;
>       privatefunction[x_]:=x^2;
>    End[]
> End[]
> Every symbol that is mentioned between the BeginPackage and Begin will
> be public, everything else will be private. When you load such a
> package, you will usually not need to explicitly use the package context
> anywhere in your code, since the package context will be on
> $ContextPath, so all public symbols of the package can be addressed
> without explicit context prefixes.
> Also note that only with a leading ` the "`Private`" context will be
> "MyPackage`Private`", otherwise the private symbols of all your packages
> will live in the same context, "Private`", which is usually exactly what
> you try to avoid by using contexts.
> > Regarding a previous post on fonts I now use:
> >    SetOptions[$FrontEnd, FontFamily->"Arial"];
> >    SetOptions[$FrontEnd, FontSize->10];
> > as soon as you ask the question, the solution suddenly becomes clear!
> If this works for you, I don't know an important reason to not do so,
> but I think the usual way to control the appearance of fonts is to
> create or change stylesheets. You usually would create your own style
> sheet, probably inherting from one that is close to what you want, and
> then, if you want it to be used as a default, set the
> DefaultStyleDefinitions option in the option inspector to use that
> stylesheet.
> hth,
> albert

Albert preceded me in replying to you, but here is my 2 cents advise

FORGET about notebook contexts or cell contexts!
These are things used by WRI developers or by people writing complex
documentation which needs to be kept somehow separated from a normal
Mathematica session.
Common mortals, including common developers, FORGET IT.

What is left? Normal packages and contexts. Do you understand them
completely? I think not yet, judging by the example Package you wrote.
Albert gave you a template package. Stick to it. Even if you do not
fully understand why it is written this way. Stick to it.
But even better, try to understand why it works.
I suggest you read Maeder's "Programming in Mathematica" (3rd ed., but
the 2nd is good enough. I use the second). It covers Mathematica 3.x or
earlier versions, but that is NOT important.
It explains the Package/Context thing "frame by frame", so to speak.
So you understand exactly what happens when Mathematica reads a Package.
Other more recent programming Mathematica books may explain the process too,
but Maeder's book is the definitive resource for me.
So to go back to your example package, you seem to attach a semantic
(that is: a meaning) to the context name. You thing a context is
public if it is called Public and private if it is called Private.
That is NOT so! You might call them Bingo and Bongo and they still
would be private. Both of them.

So again, stick to Albert's example package format and try to get
Maeder's book.

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