I came across with a line in python.
self.window.resize(*self.winsize)
What does the "*" mean in this line? I haven't seen this in any python tutorial.
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1See Unpacking Argument Lists in the online Python Tutorial.martineau– martineau2010-12-22 05:29:02 +00:00Commented Dec 22, 2010 at 5:29
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Also see stackoverflow.com/questions/4496712/….Mark Tolonen– Mark Tolonen2010-12-22 07:05:54 +00:00Commented Dec 22, 2010 at 7:05
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possible duplicate of What does ** and * do for python parameters?sth– sth2011-11-06 16:14:07 +00:00Commented Nov 6, 2011 at 16:14
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3 Answers
One possibility is that self.winsize is list or tuple. The * operator unpacks the arguments out of a list or tuple.
See : http://docs.python.org/tutorial/controlflow.html#unpacking-argument-lists
Ah: There is an SO discussion on this: Keyword argument in unpacking argument list/dict cases in Python
An example:
>>> def f(a1, b1, c1): print a1
...
>>> a = [5, 6, 9]
>>> f(*a)
5
>>>
So unpacks elements out of list or tuple. Element can be anything.
>>> a = [['a', 'b'], 5, 9]
>>> f(*a)
['a', 'b']
>>>
Another small addition : If a function expects explicit number of arguments then the tuple or list should match the number of elements required.
>>> a = ['arg1', 'arg2', 'arg3', 'arg4']
>>> f(*a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: f() takes exactly 3 arguments (4 given)
>>>
To accept multiple arguments without knowing number of arguments:
>>> def f(*args): print args
...
>>> f(*a)
('arg1', 'arg2', 'arg3', 'arg4')
>>>
Here, self.winsise is a tuple or a list with exactly the same number of elements as the number of arguments self.window.resize expects. If the number is either less or more, an exception will be raised.
That said, we can create functions to accept any number of arguments using similar trick. See this.
Comments
It doesn't have to be a tuple or list, any old (finite) iterable thing will do.
Here is an example passing in a generator expression
>>> def f(*args):
... print type(args), repr(args)
...
>>> f(*(x*x for x in range(10)))
<type 'tuple'> (0, 1, 4, 9, 16, 25, 36, 49, 64, 81)
