What's the business with the asterisk?

[mk]

Hello everyone,

From time to time I spot an asterisk (*) used in the Python code
_outside_ the usual *args or **kwargs application.

E.g. here: http://www.norvig.com/python-lisp.html

def transpose (m):
return zip(*m)

>>> transpose([[1,2,3], [4,5,6]])

[(1, 4), (2, 5), (3, 6)]

What does *m mean in this example and how does it do the magic here?

Regards,
mk

 

[Kay Schluehr]

Hello everyone,

 From time to time I spot an asterisk (*) used in the Python code
_outside_ the usual *args or **kwargs application.

E.g. here:http://www.norvig.com/python-lisp.html

def transpose (m):
   return zip(*m)
 >>> transpose([[1,2,3], [4,5,6]])
[(1, 4), (2, 5), (3, 6)]

What does *m mean in this example and how does it do the magic here?

Regards,
mk

If zip is specified as

def zip(*args):
...

one can pass zero or more arguments into zip. In the zip body one has
access to the argument tuple args. So zip(a, b, c) yields args = (a,
b, c). Now suppose you want to pass the tuple t = (a, b, c) to zip. If
you call zip(t) then args = ((a, b, c),). When calling zip(*t) instead
the tuple is passed as variable arguments just like they are specified
in the signature of zip. So args = (a, b, c).

Same holds for

def foo(**kwd):
...

and foo(**kwd) versus foo(kwd).