dict.get() - default arg evaluated even upon success

Question

Why is the default in dict.get(key[, default]) evaluated even if the key is in the dictionary?

>>> key = 'foo' >>> a={} >>> b={key:'bar'} >>> b.get(key, a[key]) Traceback (most recent call last):   File "<pyshell#5>", line 1, in <module>     b.get(key, a[key]) KeyError: 'foo' 

Answer 1

As in any function call, the arguments are evaluated before the call is executed.
In this case dict.get() is no exception...

Answer 2

use this instead

x = b.get(key) or a.get(key) 

or and and are short circuit operators, so if b has the key it won't look at a. But problems will arise if you have false values in b. If that is the case you can do:

x = b[key] if key in b else a.get(key)