5. The Wrapper Script (mod)

The script mod is a convenience script primarily for starting python3 and after its exit execute PostMØD (the summary generator). The execution can however be customised somewhat, e.g., by running python3 thorugh valgrind or gdb. At some point the script will be able to call some other virtual machine than Python, which is why the documentation will not refer directly to running python3 but instead simply say “running the selected virtual machine (VM)”. As default python3 is that VM.

The wrapper script does the following.

  1. Clear the folder out/. If it does not exist, if will be created. All printing functions in libMØD assumes out/ is created.
  2. Run the selected VM, optionally through some selected command (e.g., gdb).
  3. If the exit code of the VM is not 0, exit with that exit code.
  4. If PostMØD is not selected to be run, exit with code 0.
  5. Run PostMØD and exit with its exit code.

5.1. Usage

mod [options]
--help, -h

Shows the help output of the script.

--version, -v

Print the version of MØD and exit (the version is always printed in the start).


Do not run PostMØD after the selected VM has executed.


Run the VM through Valgrind with --tool=callgrind. This option takes precedence over the memcheck option.


Run the VM through Valgrind with standard options for memory check. If --debug is given as well, the options --vgdb=yes --vgdb-error=0 are also given to valgrind such that gdb can be connected.

--vgArgs <args>

If either --profile or --memcheck is used, this inserts <args> as an extra argument for valgrind.


Run the VM through GDB. If --memcheck is given as well, this is not the case, but GDB can then be connected to the process by the following steps:

  1. Run gdb python3 (substitute python3 for your VM).
  2. In the GDB prompt, run target remote | vgdb
  3. In the GDB prompt, run continue

Do not run any VM or PostMØD, but remove the out and summary folders.

-j <N>

Give -j <N> to PostMØD (if executed). It will pass it on to make.

-f <filename>

When python3 is the VM, execute the code include("filename").

-e <code>

When python3 is the VM, execute code (with a line break afterwards).


Use interactive mode for the Python interpreter (i.e., pass -i as additional argument), but disable the log. If ipython3 is available it will be used as interpreter, otherwise python3 is used.


Use quite mode. Certain messages are not printed.

5.2. Plugins (Loading of Additional Modules)

It can be useful to always import additional modules when using MØD. This can be achieved by writing a file in the following format:

name: <module name>
path: <Python import path>

When mod uses such a file, it will append <Python import path> to PYTHONPATH, and insert both import <module name> and from <module name> import * into the preamble. The plugin specification file must be placed in a directory that is also mentioned in the following environment variable.


A colon separated list of paths to search for plugins. Non-directory paths are skipped. All files (non-recursively) in each specified directory are checked for plugin information.

5.3. PyMØD Preamble

When the wrapper script is starting Python, it will execute a small preamble of useful code before the user-defined code is executed. The complete code, including the preamble, given to the Python interpereter can be seen in out/input after execution of the wrapper script. The preamble has the following effects.

  • Setting RTLD_GLOBAL in the interpreters dlopen flags (see Creating a Python Extension)

  • import mod and from mod import *

  • Defining the following function both in global scope and in the mod module.

    include(fName, checkDup=True, putDup=True, skipDup=True)

    Include the file fName in somewhat the same way that the #include directive in the C/C++ preprocessor includes files (e.g., handling relative paths).

    • fName (string) – the file to be included.
    • checkDup (bool) – check if the file has already been included before (with putDup=True)
    • putDup (bool) – remember that this file has been included in subsequent calls.
    • skipDup (bool) – skip inclusion instead of exiting if the file has already been included before (with putDup=True)