Append to default parameter of function

Question

is it possible to append to a default function parameter or to get the value of the function parameter from outside?

for example:

def foo(bar, foo="baz"):
    print(bar, foo)

foo("hello", "world") # print "hello world"
foo("hello", foo="world") # print "hello world" as well
foo("hello") # print "hello baz"
foo("hello", foo<append it>"bla") # how? want to print "hello bazbla"
print("default value of foo's foo parameter:", [magic here])

i dont think this is a good practise but I'm curious.

Answer 1

>>> foo.__defaults__
('baz',)

The __defaults__ attribute is documented here.

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So, to alter the foo parameter using the default value, you could use string formatting:

foo("hello", foo="{}bla".format(foo.__defaults__[0]))