What is an elegant way to select all non-None elements from parameters and place them in a python dictionary?

Question

def function(varone=None, vartwo=None, varthree=None):
     values = {}
            if var1 is not None:   
                    values['var1'] = varone
            if var2 is not None:
                    values['var2'] = vartwo
            if var3 is not None:
                    values['var3'] = varthree
            if not values:
                    raise Exception("No values provided")

Can someone suggest a more elegant, pythonic way to accomplish taking placing non-null named variables and placing them in a dictionary? I do not want the values to be passed in as a dictionary. The key names of "values" are important and must be as they are. The value of "varone" must go into var1, "vartwo" must go into var2 and so on; Thanks.

Answer 1

You could use kwargs:

def function(*args, **kwargs):
    values = {}
    for k in kwargs:
        if kwargs[k] is not None:
            values[k] = kwargs[k]
    if not values:
        raise Exception("No values provided")
    return values

>>> function(varone=None, vartwo="fish", varthree=None)
{'vartwo': 'fish'}

With this syntax, Python removes the need to explicitly specify any argument list, and allows functions to handle any old keyword arguments they want.

If you're specifically looking for keys var1 etc instead of varone you just modify the function call:

>>> function(var1=None, var2="fish", var3=None)
{'var2': 'fish'}

If you want to be REALLY slick, you can use list comprehensions:

def function(**kwargs):
    values = dict([i for i in kwargs.iteritems() if i[1] != None])
    if not values:
        raise Exception("foo")
    return values

Again, you'll have to alter your parameter names to be consistent with your output keys.