Loop function parameters for sanity check

Question

I have a Python function in which I am doing some sanitisation of the input parameters:

def func(param1, param2, param3):
    param1 = param1 or ''
    param2 = param2 or ''
    param3 = param3 or ''

This caters for the arguments being passed as None rather than empty strings. Is there an easier/more concise way to loop round the function parameters to apply such an expression to all of them. My actual function has nine parameters.

Answer 1

This looks like a good job for a decorator. How about this:

def sanitized(func):
    def sfunc(*args, **kwds):
        return func(*[arg or '' for arg in args],
                    **dict((k, v or '') for k,v in kwds.iteritems()))
    sfunc.func_name = func.func_name
    sfunc.func_doc = func.func_doc
    return sfunc

You would use this on your function like so:

@sanitized
def func(param1, param2, param3):
    print param1, param2, param3

Then the parameters will be replaced by the empty string if they are false:

>>> func('foo', None, 'spam')
foo  spam

(Note that this will still mess up the function signature as Ned Batchelder points out in his answer. To fix that you could use Michele Simionato's decorator module-- I think you'd just need to add a @decorator before the definition of sanitized)