How does garbage collection happen in Python

Question

I am new to Python. I want to know how does the garbage collection algorithm work in Python?

Answer 1

The Garbage collection runs automatically as the program is under execution, sometimes, we might want to run the Garbage collection at a specific time. We can do this by calling collect() function. Let’s try to define a LinkedList class to demonstrate this:

class LinkedList(object):
    def __init__(self, name):
        self.name = name
        self.next = None
    def set_next(self, next):
        print('Linking nodes %s.next = %s' % (self, next))
        self.next = next
    def __repr__(self):
        return '%s(%s)' % (self.__class__.__name__, self.name)

Once that is done, we can start constructing their objects and trigger Garbage collection manually:

# Constructing a circular LinkedList
a = LinkedList('1')
b = LinkedList('2')
c = LinkedList('3')
a.set_next(b)
b.set_next(c)
c.set_next(a)

# Remove references to the LinkedList nodes in this module's namespace
a = b = c = None

# Show the effect of garbage collection
for i in range(2):
    print('Collecting %d ...' % i)
    n = gc.collect()
    print('Unreachable objects:', n)
    print('Remaining Garbage:', pprint.pprint(gc.garbage))
    print

When we run this, the output will be:

In this example, the cyclic LinkedList objects are cleared as soon as garbage collection runs the first time.