CODEWITHSUNDEEP
pythonrefcounting
user744629
user744629

Reputation: 2041

Python reference count

In the following Python code:

class Foo:
    def bar(self):
        return 1

def baz():
    return Foo()

print baz().bar()

Question 0:

When bar() is evaluated in print baz().bar(), what make the Foo instance returned by baz() to have not yet been garbage collected, since it seems there is no reference to it, like there would be in:

foo = baz()
print foo.bar()

where foo store a reference of the Foo instance.

Question 1:

If Foo and baz were implemented in C in a Python extension module, should baz increment the reference count of the returned object foo to set it to 1?

Upvotes: 2

Views: 420

Answers (2)

JamesNoonan33
JamesNoonan33

Reputation: 584

For part 0: Each time baz is called it creates a new object, Foo. You could see this by adding an init to Foo. So, before the print, the Foo instance does not exist. (It is not created when the function baz in declared, but only when it's called.

Part 1: As with 0, declaring baz() does not create an object. Calling baz() does. The reference count is incremented when 'Foo()' (Constructor) is called every time function baz is called.

Upvotes: 0

shx2
shx2

Reputation: 64298

Answer 0: when bar() is called, bar is a bound method (bound to the Foo instance), which keeps a reference to its self argument, which is the Foo instance.

Upvotes: 3

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