how to load virtualenv using environmental module file (tcl script)?

Question

I am trying to write a module file for a program that creates a python virtualenv. In order to start the virtualenv, it needs to first run /programs/program-env/bin/activate. How do I do this in a modulefile? Any help will be greatly appreciated.

Note: I tried just putting the above line in the file and it didn't work.

Thanks,

Edit:

I am writing a modulefile to load a program that can only run in a virtualenv. Normally these modulefiles will set variable names and/or add bin directory to path. Since the above package is somewhat different, I don't know how to proceed. An example module file can be found here.

Answer 1

Here is a slightly more complete answer, building on the answers by Donal and betapatch, that allows you to swap between two modules which do similar things:

if { [module-info mode load] || [module-info mode switch2] } {
    puts stdout "source /programs/program-env/bin/activate;"
} elseif { [module-info mode remove] && ![module-info mode switch3] } {
    puts stdout "deactivate;"
}

Firstly, you need to use source .../activate rather than just .../activate.

Secondly, modules has some horrible logic when swapping modules. If you want to module swap foo bar (remove foo and load bar in its place), it actually does the following:

foo: switch1 # prep for remove
foo: remove  # actually remove
bar: switch2 # load new module
foo: switch3 # cleanup
foo: remove  # happens at the same time as foo switch3

This means that if foo and bar are both modulefiles using virtualenvs, the second foo remove will deactivate bar.

Answer 2

The Modules system is pretty strange, since what it's really doing is creating a set of instructions that are evaluated by the calling shell. This means that normal Tcl ways of doing things are often not quite right; it is the caller who needs to run /programs/program-env/bin/activate, not the Tcl script.

The first thing to try is:

system "/programs/program-env/bin/activate"

However, looking between the lines in the FAQ, I see that you probably would need to do this (with guards):

if {[module-info mode] == "load"} {
    puts stdout "/programs/program-env/bin/activate"
}

I have no idea how to reverse the operation (which is part of the point of a module).