Python方法默认基于__init__ args类

Question

I want my methods defaults within a class to be set to what was passed in through the __init__ method. Something like this:

class Foo(object):

    def __init__(self, loc=None):
        self.loc = loc

    def test(self, loc=self.loc):
        print loc


test = Foo()
test.test()
>>> None

test = Foo('foobar')
test.test()
>>> foobar

Is this possible or another way of achieving this?

EDIT: I know this current code is not possible but something that would function like this is what I'm looking for.

Thanks

Answer 1

Default argument values are evaluated at the point of function definition in the defining scope, but self is an argument only available during function call.

See an example:

i = 5
def f(arg = i): print arg
i = 6
f()

will print 5. Visualization on python-tutor.

It is a common pattern to default an argument to None and add a test for that in the code:

def test(self, loc = None):
    if loc is None:
       loc = self.loc
    print loc

Answer 2

Do something like this:

def test(self, loc = None):
    if loc is None:
       loc = self.loc