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Re: The difference between Needs[ ] & Get[ ]

  • To: mathgroup at
  • Subject: [mg40158] Re: [mg40149] The difference between Needs[ ] & Get[ ]
  • From: "neuron" <b90401114 at>
  • Date: Sun, 23 Mar 2003 04:12:55 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Thanks a lot for detailed answer.

As to this problem,
may I say that Get[ ] can load a file though the context "ComplexMap" in 
BeginPackage[ ] and the filename ComplexMap1 are not the same,
but Needs[ ] cannot ?
If so, what are the internal difference which make this result between 
Get[ ] & Needs [ ] ?
I apologize in advance for my poor English.

----- Original Message -----
From: "David Park" <djmp at>
To: mathgroup at
Subject: [mg40158] RE: [mg40149] The difference between Needs[ ] & Get[ ]

> neuron,
> The reason that ComplexMap1 does not load is that Roman has not set it up as
> a package that can load. You can only look at it as a text file to see what
> an early version of the package looked like. That is because he has the
> Begin statement:
> BeginPackage["ProgrammingInMathematica`ComplexMap`"]
> and it should be
> BeginPackage["ProgrammingInMathematica`ComplexMap1`"]
> to be correct for loading. "ProgrammingInMathematica" gives the folder name
> and "ComplexMap1" would give the specific file name.
> He intends that you actually use the ComplexMap package. (You could also use
> Graphics`ComplexMap`.)
> The advantage of the Needs statement over Get is that it can be reevaluated
> and if the package is already loaded it will do nothing. Many packages
> cannot be loaded a second time without generating error messages. It is
> generally more convenient to use Needs. For example, if you open two
> different notebooks that both use the same package and both have
> initialization cells to load the package, the package will only be loaded
> once.
> David Park
> djmp at
> From: neuron [mailto:b90401114 at]
To: mathgroup at
> Hello MathGroup gurus,
> I am new to Mathematica and now reading "Programming In Mathematica."
> I am a little  confused with Needs[ ] & Get[ ].
> I kow that  Needs[ ] checks $Packages whether the package is present or
> not and I usually use Needs[ ] to load a package.
> On the xiv page of "ProgrammingInMathematica" it says "Even better is
> Needs["ProgrammingInmathematica`Package`"]........"
> but on page 13,
> when I input
> Needs["ProgrammingInMathematica`ComplexMap1`"]
> instead of
> <<ProgrammingInMathematica`ComplexMap1`
> an error occurs:
> Needs::nocont: Context ProgrammingInMathematica`ComplexMap1` was not
> created when Needs was evaluated.
> I don't know why, for the Help says "Needs["context`"] calls
> Get["context`"]. By convention, the file loaded in this way is the one
> which contains a package that defines context`. "
> I execute Mathematica 4.1 on Windows98
>  Thanks for any advice.

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