#!/usr/bin/env python
import traceback
from typing import Optional
from string import Template

class ParameterMismatchError(Exception): pass
class ModusMismatchError(Exception): pass


def fill(s: str, modus: Optional[str]=None, **kwargs: dict[str, str]) -> str:
    if modus is not None:
        dummy = s.format(modus=modus)
        if dummy == s: # no change!
            raise ModusMismatchError('modus (%s) given, but not replaced!'%(modus))
        s = dummy
    t = Template(s)
    if t.get_identifiers() != list(kwargs.keys()):
        raise ParameterMismatchError('template wants %s, but function call has %s'%(
            t.get_identifiers(), list(kwargs.keys())))
    return t.substitute(**kwargs)


def run(s: str) -> None:
    # versucht einige Ersetzungen fängt gibt eventuelle Fehler aus
    try:
        print(fill(s))
    except Exception as e:
        traceback.print_exc()
        
    try:
        print(fill(s, 'BLA'))
    except Exception as e:
        traceback.print_exc()
        
    try:
        print(fill(s, 'BLA', a=1, b=2))
    except Exception as e:
        traceback.print_exc()

    ### oder kurze Fehlerausgaben anstelle von traceback.print_exc():
    # except ParameterMismatchError as e:
    #     print('%s: %s'%(e.__class__.__name__, str(e)))
    # except ModusMismatchError as e:
    #     print('%s: %s'%(e.__class__.__name__, str(e)))
        

if __name__ == '__main__':
    run('eins:MODUS:zwei')    
    run('eins:{modus}:zwei $a $b')