I am sort of new to Python so I was reading through Pro Python and it had this section about passing variable keyword arguments to function. After reading that section I wrote the following code which doesn't seem to work.
def fun(**a):
return a['height'] if a is not {} else 0
I got a key error when I called fun with no arguments. How should I change the code so that it returns a['height'] if a is not a null dictionary and returns 0 if it is a null dictionary?
You are testing if a the same object as a random empty dictionary, not if that dictionary has the key height. is not and is test for identity, not equality.
You can create any number of empty dictionaries, but they would not be the same object:
>>> a = {}
>>> b = {}
>>> a == b
True
>>> a is b
False
If you want to return a default value if a key is missing, use the dict.get() method here:
return a.get('height', 0)
or use not a to test for an empty dictionary:
return a['height'] if a else 0
but note you'll still get a KeyError if the dictionary has keys other than 'height'. All empty containers test as false in a boolean context, see Truth Value Testing.
To check if a dictionary has a specific key, do this:
if 'height' not in a: return 0
Or you can use get() with a default:
return a.get('height', 0)
