检查存在和是否存在是一定的值

Question

I frequently need to check if an instance of a class has a property and if that property exists, make a comparison with its value. Is there no way to do it besides the following?

if house.garage:
    if house.garage == '3 car':
        # do something with house.garage

Answer 1

Instead of using the dot notation, you can make a call to getattr , which can return a default value if the named attribute does not exist:

if getattr(house, 'garage', "") == '3 car':
    # proceed

If house does not have an attribute named 'garage', getattr just needs to evaluate to something that does not equal '3 car'.

Answer 2

You can "consolidate conditional expression" as outlined by Martin Fowler here: http://sourcemaking.com/refactoring/consolidate-conditional-expression#permalink-15

Essentially, any if statement that contains another if statement inside it is really just 1 if statement with an and in between!

if house.garage:
    if house.garage == '3 car':
        # do something with house.garage

becomes

if house.garage and house.garage == '3 car':
    # do something with house.garage