How to avoid running code when a script is imported as a package?

Question

In Python, the boilerplate line if __name__ == "__main__": defines a code block that should be executed when the code is run as a script, but not when imported as a module.

Is there a way to do this using Mathematica's .wls scripts?

To clarify, I want to designate part of my code to be run only when the script is run in an interactive session or from the command line (e.g. using wolframscript), but not when the code is imported into another notebook/script using Get or similar.

Answer 1

You may be able to use $EvaluationEnvironment to check notebooks vs. Scripts.

If you are trying to check against whether it is the main file or not $Input may be useful. It should be set when Get-ing a file or similar. So the check If[$Input==="", ...] may work for you.

Answer 2

This works on my Windows machine (not sure how well it translates to Mac and Linux yet):

Place this in a file called test.wls:

checks = { $Notebooks, Length[$CommandLine]===1, MemberQ[$CommandLine,"-wlbanner"], MemberQ[$CommandLine,"-noicon"] };
Print @ Switch[
 checks,
 {True,False,False,True}, "Running in notebook interface",
 {False,True,False,False}, "Running in wolfram.exe",
 {False,False,True,False}, "Running in wolframscript.exe",
 {False,False,False,False}, "Running in test.wls"
];

Then run this file in different modes. First as a script:

C:\Users\arnoudb.WRI>test.wls
Running in test.wls

Then using wolframscript.exe:

C:\Users\arnoudb.WRI>wolframscript
Wolfram Language 11.3.0 Engine for Microsoft Windows (64-bit)
Copyright 1988-2018 Wolfram Research, Inc.

In[1]:= Get["test.wls"]
Running in wolframscript.exe

Then using wolfram.exe:

C:\Users\arnoudb.WRI>"C:\Program Files\Wolfram Research\Mathematica\11.3\wolfram.exe"
Mathematica 11.3.0 Kernel for Microsoft Windows (64-bit)
Copyright 1988-2018 Wolfram Research, Inc.

In[1]:= Get["test.wls"]
Running in wolfram.exe

And finally from a notebook interface:

Get["C:\\Users\\arnoudb.WRI\\test.wls"]

Running in notebook interface

Probably needs some work to get this more solid.

Answer 3

The way that works is that when Python runs a source file as the main program, it first sets the variable __name__ to "__main__" (see this answer). As far as I know, Mathematica does no such thing for you, so unless you want to require every source file to include code to replicate that behavior, the closest I can think of is to have the script check if it is being evaluated as part of a Get or Needs expression. Something like:

If[
    MatchQ[Stack[], {___, Get|Needs, If, MatchQ}],
    Print["this will evaluate if being imported by Get or Needs"],
    Print["this will evaluate otherwise"]
]

That being said, I wouldn't really recommend writing code like this and would rethink if this behavior is really necessary.