Jach Fong <jf...@ms4.hinet.net> writes: > ... > 4.7.4. Unpacking Argument Lists > The reverse situation occurs when the arguments are already in a list or > tuple but need to be unpacked for a function call requiring separate > positional arguments. > ... >>>> args = [3, 6] >>>> list(range(*args)) > """ > > I can't understand why line 19 works?
Not sure what "line 19" is - but if it refers to the example above: "range" accepts (among others) 2 integer arguments. The "*args" above means: unpack the sequence in "args" into individual arguments. This means (with the values of the example above), that "range(*args)" is equivalent to "range(3, 6)". > Didn't it violate the rule of > "# non-keyword argument after a keyword argument"? No keyword arguments at all in the above example. > and why a more > reasonable look syntax gets an error? > > action(*args, progress) > ^ > SyntaxError: only named arguments may follow *expression File > "test.py", line 19 This is (in my view) a somewhat arbitrary restriction -- maybe introduced for symmetry with the function definition syntax. The message is quite clear, however: after the "*arg", you must pass keyword arguments only, i.e. they must have the form "param=value". > The only reason I can guess is that it checks with the rule in 4.7.3 > which is really unrelated. The "*any" notation used in different places > with different meaning, such as defining arbitrary argument, unpacking > argument or even in an assignment(a,*b=any). Maybe it will be better to > stop this syntax checking and lets both statements below valid:-) The "*args" and "**kw" are very helpfull. I hope (and expect) they will remain. -- https://mail.python.org/mailman/listinfo/python-list
