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The details are as follows:

A = 1

An is a reference and 1 is an object. Python caches integers and short strings, with only one object, but long strings and other objects (list dictionaries) have many objects (assignment statements create new objects).

From sys import getrefcounta= (getfrecount (a)) print

Return 4, when a reference is passed to getfrecount as a parameter, a temporary reference is created, + 1.

Object reference object

Class from_obj (object): def _ init__ (self, to_obj): self.to_obj = to_objb = [1Mae 2jue 3] a = from_obj (b) print (id (a.to_obj)) print (id (b)) c = [BMIT b]

A refers to the object b _ ~ C references b twice.

Comb through the reference topology through the objgraph package (previously installed with xdot).

X = [1,2,3] y = [x, dict (key1=x)] z = [y, (x, y)] import objgraphobjgraph.show_refs ([z], filename='ref_topo.png')

Never refer two objects to each other or yourself, and form a reference ring to cause trouble to the garbage collection mechanism.

Garbage collection

Recycle objects with a reference count of 0. When garbage collection, python can not do other tasks, reduce efficiency, so it is not always garbage collection. Python records allocation objects (object allocation) and de-allocation objects (object deallocation), and the difference is higher than a certain threshold to start recycling.

Import gcprint (gc.get_threshold ())

(700, 10, 10) 700 is the threshold, and two 10s are generation-related thresholds, which are reset by set_threshold (). Manually enable garbage collection gc.collect ().

Generation by generation recovery

Basic assumption: the longer you live, the less likely you are to become rubbish.

The subjects were divided into three generations: 0, 1, 2 and 3. New object 0 generation, after a garbage collection is still alive to the next generation. All 0 generations must be scanned when garbage collection is started. If 0 generations pass through a certain number of garbage collections, 0 and 1 generations will be scanned. Similarly, 0 and 2 generations will be scanned. The results showed that 10 times 0 generation and 10 times 1 generation and 10 times 1 generation and 2 generations respectively.

Isolated reference ring

Originally, the reference is deleted after the two table objects reference each other, but the object reference count part 0 will not be recycled.

Then python copies each object reference count, traverses all object j referenced by object I for an object I, and subtracts gc_ref_j by 1. 0.

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