I am calling a function
foo(x,y0=y[0],y1=y[1],y2=y[2],...,y<d>=y[<d>])
where <d> is a large number that may vary from call to call. All arguments except x are keyword arguments.
I didn't write foo myself, so I cannot just pass y as a list instead. Is there an automated way to split a list into keyword arguments?
First, build a list of name, value pairs, then convert that to a dictionary and pass it to the function.
y_vals = [ 1, 2, 3, 'a', 'b', 'c' ]
arg_dict = dict(('y%d' % i, v) for i, v in enumerate(y_vals))
foo(x, **arg_dict)
arg_dict = { 'y%d' % i: v for i, v in enumerate(y_vals)}
Use * for passing unpacked arguments from a list, You can send in normal arguments in place of keyword arguments, just make sure you pass them in proper order, for e.g:
def foo(x, y1=None, y2=None, y3=None, y4=None, ... , yN=None):
# func stuff
You can pass a list to the function unpacked, like:
arguments = ["arg-y1", "arg-y2", "arg-y3", ... , "arg-yN"]
foo (x, *arguments)
As they are keyword arguments, they will have some default value.
If you want to pass only a few specific values, you can use the Dictionary and ** for kw:
kwargs = {"y1": "arg-y1", "y3": "arg-Y3" }
foo (x, **kwargs)
You can use **kwargs to let your functions take an arbitrary number of keyword arguments ("kwargs" means "keyword arguments"):
>>> def print_keyword_args(**kwargs):
... # kwargs is a dict of the keyword args passed to the function
... for key, value in kwargs.iteritems():
... print "%s = %s" % (key, value)
...
>>> print_keyword_args(first_name="John", last_name="Doe")
first_name = John
last_name = Doe
You can also use the **kwargs syntax when calling functions by constructing a dictionary of keyword arguments and passing it to your function:
>>> kwargs = {'first_name': 'Bobby', 'last_name': 'Smith'}
>>> print_keyword_args(**kwargs)
first_name = Bobby
last_name = Smith
The Python Tutorial contains a good explanation of how it works, along with some nice examples.
For your case to convert list to keyword arguments :
# y is a list with arguments stored.
kwargs = {}
for arg in range(len(y)):
kwargs['y'+str(arg)] = y[arg]
foo(**kwargs)
