Python memory managment. Deeping in Garbage collector

José Manuel Ortega
@jmortegac
Python Memory
Management 101
Deeping in Garbage collector

About me
● @jmortegac
● http://jmortega.github.io
● https://www.linkedin.com/in/jmortega1/

Agenda
● Introduction to memory management
● Garbage collector and reference counting
with python
● Review the gc module for configuring the
python garbage collector
● Best practices for memory managment

Introduction to memory management
● Memory management is the process of
efficiently allocating, de-allocating, and
coordinating memory so that all the
different processes run smoothly and can
optimally access different system
resources.

Heap allocation
def main():
x=300
print(id(x))
w=fun(x)
print(id(w))
def sqr(x):
print (id(x))
z=x*x
print(id(z))
return z
if __name__ == "__main__":
main()

Python Objects in Memory
● Each variable in Python acts as an object
● Python is a dynamically typed language
which means that we do not need to
declare types for variables.

Reference counting
● Python manages objects by using reference
counting
● Reference counting works by counting the
number of times an object is referenced by
other objects in the application.
● When references to an object are removed,
the reference count for an object is
decremented.

Reference counting
● A reference is a container object pointing at
another object.
● Reference counting is a simple technique
in which objects are allocated when there is
reference to them in a program

Reference counting
● when reference count increases?
○ x=1
○ def(x):
○ list.append(x)

Reference counting
● Easy to implement
● Objects are immediately deleted when
reference counter is 0
✗ Not thread-safe
✗ Doesn’t detect cyclic references
✗ space overhead - reference count is
stored for every object

Python Garbage collector
● The Python Garbage Collector (GC) runs
during the program execution and is
triggered if the reference count reduces to
zero.

Python Garbage collector
● Reference Counting + Generational GC
● RefCount reaches zero, immediate
deletion
● Deleted objects with cyclic references
are deleted with Tracing GC

Garbage collector(GC) reference cycle

>>> def ref_cycle():
... list = [1, 2, 3, 4]
... list.append(list)
... return list

import gc
for i in range(8):
ref_cycle()
n = gc.collect()
print("Number of unreachable objects collected by GC:", n)
print("Uncollectable garbage:", gc.garbage)
print("Number of unreachable objects collected by GC:",
gc.collect())

Python Object Graphs
https://mg.pov.lt/objgraph/
>>> x = []
>>> list = [x, [x], dict(x=x)]
>>> import objgraph
>>> objgraph.show_refs([y],
filename='sample-graph.png')

Best practices for memory managment
● Using gc.collect() carefully
print("Collecting...")
n = gc.collect()
print("Number of unreachable objects collected:", n)
print("Uncollectable garbage:", gc.garbage)

● Using with context manager for working
with files
with open('data.txt', 'r') as file:
data = ','.join(line.strip() for line in file)

● Avoid List Slicing with [:]
list= [1,2,3,4]
list[1:3]
list[slice(1,3)]

● String Concatenation
string= “hello”
string+= “world”
wordList = ("hello", "world")
string = " ".join(wordList)

● Use Iterators and Generators

References
● https://stackabuse.com/basics-of-memory-management-in-p
ython/
● https://realpython.com/python-memory-management
● https://rushter.com/blog/python-garbage-collector
● https://pythonchb.github.io/PythonTopics/weak_references.
html

https://www.youtube.com/c/JoseManuelOrtegadev

https://speakerdeck.com/jmortega

Python memory managment. Deeping in Garbage collector

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