python - elegant unpacking variable-length tuples -

a real, if silly problem:

https://github.com/joshmarshall/tornadorpc/blob/master/tornadorpc/base.py

def start_server(handlers, ...):     ...     (route, handler) in handlers:         ... 

normally "handlers" list of 2-element tuples. particular solution (tornado) can pass third argument particular handler (kw args). tuple in "handlers" may have 2 elems or 3 elems other times.

i need unpack in loop. sure, can smth length checking or try..except on unpacking. ugh.

can think of smth better/more clever this:

in [8]: handlers out[8]: [(1, 2), (3, 4, 5), (6, 7)]   in [9]: new_handlers = [x + (none,) x in handlers] 

?

if handler takes keyword arguments, use dictionary third element:

handlers = [(1, 2, {}), (3, 4, {'keyword': 5), (6, 7, {})]  route, handler, kwargs in handlers:     some_method(route, handler, **kwargs) 

or can apply arguments using *args syntax; in case catch all values in loop:

for args in handlers:     some_method(*args) 

if have unpack @ least 2 arguments, in separate step:

for handler in handlers:     route, handler, args = (handler[0], handler[1], handler[2:]) 

where args tuple of 0 or more elements.

in python 3, can handle arbitrary width unpacking splat (*) target:

for route, handlers, *args in handlers: 

where *args captures 0 or more extra values in unpack.

the other route, elements in handlers minimal length done with:

[(h + (none,) * 3)[:3] h in handlers] 

demo:

>>> handlers = [(1, 2), (3, 4, 5), (6, 7)] >>> [(h + (none,) * 3)[:3] h in handlers] [(1, 2, none), (3, 4, 5), (6, 7, none)]