[GRASS-user] a question on how to split python code in multiple modules

GRASS GRASS user
1

Pythonians (2),

I am pythonising a rather long grass-bash script.

I try to split it in smaller python modules. Each module starts a
definition of the main function and ends with the 'if __name__ ==
"__main__":' trick (e.g. code below).

* Is this the way to go?

The first independent "module" contains a series of variables required
for the rest of the modules to run. However, I have difficulties to
understand clearly how to load it so the variables are available to the
rest of the modules. It loads fine but the actual variables (such as
literal strings, lists, etc.) are no where to be found. I probably do
some beginner's mistake here. I am sea

* How do I instruct Python to keep variables in memory after executing
the function?

Also, I've seen in several grass70 python scripts, in the end of the
main() function and before the _trick_, "sys.exit(0)" calls or "return
0" code.

* What does this actually do? Is this mandatory?

I know these questions are generic but I don't know if there are grass-y
details to pay attention to. Regards, Nikos

--%<--variables-->%--
# comments

# define main function
def main():

# define variables, lists, etc.
reference = "reference_map"
high_resolution = 30
low_resolution = 500
thresholds = range(10, 110, 10)
# ...

# make this module both reusable and independent
if __name__ == "__main__":
    options, flags = grass.parser()
    main()

--%<-----end----->%--

2

Nikos Alexandris wrote:

I am pythonising a rather long grass-bash script.

I try to split it in smaller python modules. Each module starts a
definition of the main function and ends with the 'if __name__ ==
"__main__":' trick (e.g. code below).

* Is this the way to go?

Generally, no.

The '__name__ == "main"' check is used to determine whether a Python
file is being run as a program rather than being imported as a module.

A large program should have a single executable file with the rest
being imported.

You might start by producing a single Python script, then ask for
advice about splitting it up once you have working code.

The first independent "module" contains a series of variables required
for the rest of the modules to run. However, I have difficulties to
understand clearly how to load it so the variables are available to the
rest of the modules. It loads fine but the actual variables (such as
literal strings, lists, etc.) are no where to be found. I probably do
some beginner's mistake here.

The top-level __main__ module is the last place that you should be
defining global variables, as these won't be readily accessible from
imported modules.

Instead, either put the variables in a module (e.g. "core"), and have
the various modules import that, or put them in whichever module uses
them. If module A imports module B, A can reference B's definitions
but B can't (easily) reference A's definitions.

* How do I instruct Python to keep variables in memory after executing
the function?

Variables which are written to within a function before they are read
are local by default. If you want to modify a global variable within a
function, use the "global" statement beforehand.

Also, I've seen in several grass70 python scripts, in the end of the
main() function and before the _trick_, "sys.exit(0)" calls or "return
0" code.

* What does this actually do? Is this mandatory?

sys.exit() terminates the process. It shouldn't actually be necessary;
reaching the end of the program without error should have the same
effect.

--
Glynn Clements <glynn@gclements.plus.com>