So, a more complete example might help: def myFunc(par=None): if par: # do whatever is needed when the parameter exists pass #finish proces

So, a more complete example might help: def myFunc(par=None): if par: # do whatever is needed when the parameter exists pass #finish processing This allows you to pass in [], {}, None, '', or omit par all together, which will all behave as if par=None, or pass in data and use it appropriately. You can also use if not par: pass if you want to do the inverse.