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Set variables to output based on regex on swig

I have a C++ library that I want to use in Python with SWIG. Many functions in that library have output arguments, arguments I have to set manually as OUTPUT.
The thing is these arguments are prefixed with "ao_" (argument output).
Is there a way to set every arguments prefixed with "ao_" to OUTPUT ?

argparse nargs and positionals

This is a program that already exists and I'm trying to extend it - so my hands are tied somewhat :-(.
I have a program where I want to add an option that takes an unknown number of values so I'm trying to use nargs='+'. I can spot when a value is not actually for my option and is a positional argument and I can then use setattr to set the positional argument - but argparse doesn't get a chance to find the positional argument itself so complains.
The syntax for the command, as show in arparse generated help text, is
command [--option value [value...]] positional
In theory this is possible if I did this instead
command positional [--option value [value...]]
This is precisely how examples, even in the argparse documentation, work but that is NOT how the command is currently used, NOT how users typically provide programs with options and NOT how argparse generated help text shows the expected syntax.
So it there a way to somehow both handle the positional but also tell argparse 'oh, I found this positional so no need to complain that it is missing'?

Format of responses to help() in Python shell

I have a question about how certain "help()" items show up in my Python 3.6.2 IDLE shell running on Windows. From the docs, I'd expect to see sum(iterable[, start]) and pow (x, y[, z]), but calling help on those yields sum(iterable, start=0, /) , and pow(x, y, z=None, /). There may be other functions that display the same way.
I'm curious about why they put the descriptor in keyword form (which you cannot use explicitly when calling the functions, as doing so throws a "x takes no keyword arguments" error), but mostly, what is the slash doing there?

[Adding a bit to the linked answer...]
In Python3, documentation of optional args in signatures was changed from brackets, as in '[, start]' (with the default hopefully given in the docstring) to directly giving the default, as in 'start=0'. Sometime later (perhaps 3.4), '/' was (gradually) added to the signature of C-coded functions that do not allow passing an argument by keyword. Before this, there was no easy way to discover the fact without trial and exception. (I believe that there are a few optional args that do not have a default. These have to continue with brackets.)
None of this has anything to do with IDLE, which prints help() output as received. That is why I removed the tag. However, IDLE for current 3.6 and 3.7 adds the following to tooltips when the signature contains '/'.
['/' marks preceding arguments as positional-only]
I don't know if help() should do the same.

Postion of argument will be fixed

in command line if I run my program
python parse.py config=abc.txt factor_date=20151001 like this
I want the position of argument will be fixed. That means if I pass argument like below
python parse.py factor_date=20151001 config=abc.txt
it has to show error.
import sys
config_file=sys.argv[1]
factor_date = sys.argv[2]
argstring=""+config_file+" "+factor_date+""
arg_list = argstring.split(' ')
input={}
for arg in arg_list:
#x=arg.split("--")
key,val=arg.split("=")[0],arg.split("=")[1]
if key == "config":
input[key]=val
if key =="factor_date":
input[key]=val
print input

You can have a look at click. It let's you create command line interfaces pretty much effortlessly. It's bases on using decorators.

You should have a look at argparse. Your use case is for positional arguments. If you specify the name of the argument (optional arguments with argparse) then it does not make sense to force a specific order.
Still, when using positional arguments one could call the program with worng arguments, you will have to check by yourself the values provided by the user. However, you can force a type and it will automagically convert the strings, which in the case you describe would solve the problem.

How do I configure required arguments while still allowing special arguments like "--version"?

I have a Python script that accepts one or more input files and produces one or more output files (sort of a compiler, translating one syntax into another)
In my argparse section, I have configured so that the list of input files option is "nargs='+'", so that it will show a "too few arguments" error if user provides zero input files.
At the same time, I want to have a "--version" option that will just print the current script version and exit. When this option is provided, everything else (if provided) is irrelevant and should be ignored.
Just like ArgumentParser automatically adds the "--help" option which works like this, how can I add a "--version" option without changing the nargs='+' mechanism?

Try the version action class. From the docs:
'version' - This expects a version= keyword argument in the add_argument() call, and prints version information and exits when invoked:
>>>
>>> import argparse
>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('--version', action='version', version='%(prog)s 2.0')
>>> parser.parse_args(['--version'])
PROG 2.0
It behaves like the help (-h) except it displays the version parameter that you define with it (or lacking that a version value that you give the parser itself).