dict.pop or dict.get and evaluation

Consider the following code:

>>> def default_answer():
...     print "Default was required!"
...     return 100
... 
>>> g = { 'name': 'Jordan', 'age': 35 }
>>> result = g.get('age', default_answer())
Default was required!
>>> result = g.pop('age', default_answer())
Default was required!

Notice that whether g contains the expected key or not, default_answer is called. This makes sense programmatically but if default_answer was computationally expensive this would be a hassle (to run a lot of code to create a value that was going to be thrown away).

The only way I can think of writing this without always calling default_answer is:

result = g.pop('age', False) or default_answer()

Is this the best way to do it?

(Note that I'm aware that replacing default_answer with an object with lazy evaluation would also solve part of this problem, but that's outside the scope of this question).

No, this is not the best way to do this, since the result of g.pop() might be "falsy". Use try/except instead:

try:
    result = g.pop('age')
except KeyError:
    result = default_answer()

This idiom is called EAFP and is usually preferred over LBYL for various reasons:

1. It avoids looking up the key twice (which is not an issue with an actual dict, but might be suboptimal with other mappings).

2. It avoids a race condition in threaded code.

3. Many people find it easier to read.