Generate permutations in python

permute.py

# dependencies

from typing import Union, List, Generator

# permute method

def permute(options:Union[str,List], places:int=None) -> Generator[List,None,None]:
    """Generate all permutations recursively.
    
    Args:
        options = list of possible values per place
        
        places = number of places; default=len(options)
    
    Yields:
        a permutation, being length places, each element being an element 
        from options
    """
    
    on:int = len(options)
    if places is None:
        places = on
        
    elif places > on:
        raise Exception('error: can not permute {} over more than {} places'.format(
            options,
            on
        ))
    
    for oi in range(on):
        # select option for first place
        o:Any = options[oi]
        
        if places > 1:
            suboptions:List = options[:oi] + options[oi+1:]
            
            if len(suboptions) == 1:
                yield [o, suboptions[0]]
                
            else:
                # permute latter places recursively
                for suffix in permute(suboptions, places-1):
                    yield [o] + suffix
    
        else:
            # no more places to compute
            yield [o]
    # end for oi in range(on)
# end permute