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20220501153651-interning_optimization.org

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+:PROPERTIES:
+:ID:       c0d562c7-9d2f-4f35-b7b1-f6b6ca5273f9
+:mtime:    20220501162112
+:ctime:    20220501153651
+:END:
+#+title: Interning optimization
+
+* Introduction
+ * Concerne /CPython/,
+ * Consiste en la *réutilisation* d'objet plutôt que d'en recrééer.
+
+* Integer interning
+ * Au démarrage, /CPython/ pré-charge en mémoire les entiers de *-5 à 256*,
+ * A chaque fois qu'un entier compris dans cet intervalle est utilisé, celui-ci fait référence à un entier pré-chargé.
+#+BEGIN_SRC python :results output
+a = 100
+b = 100
+
+print(f'Memory address of a: {id(a)}')
+print(f'Memory address of b: {id(b)}')
+print(f'a is b: {a is b}')
+#+END_SRC
+
+#+RESULTS:
+: Memory address of a: 9792128
+: Memory address of b: 9792128
+: a is b: True
+ 
+* String interning
+ * Au démarrage, /CPython/ pré-charge en mémoire les chaines de caractères présentes dans le code et de longueur *<=
+   4096*,
+ * Il est possible de forcer le pré-chargement en mémoire d'une chaine à l'aide de ~sys.intern~
+
+#+BEGIN_SRC python :results output
+from random import choice
+from string import printable
+from sys import intern
+
+a = "Data"
+b = "Data"
+
+print(f'Memory address of a: {id(a)}')
+print(f'Memory address of b: {id(b)}')
+print(f'a is b: {a is b}')
+
+c = intern(''.join(choice(printable) for _ in range(4097)))
+d = c
+
+print(f'Memory address of c: {id(c)}')
+print(f'Memory address of d: {id(d)}')
+print(f'c is d: {c is d}')
+#+END_SRC
+
+#+RESULTS:
+: Memory address of a: 139629084500336
+: Memory address of b: 139629084500336
+: a is b: True
+: Memory address of c: 28459264
+: Memory address of d: 28459264
+: c is d: True
+
+* Références
+ * [[https://pythonsimplified.com/optimization-in-python-interning/][Optimization in Python — Interning - pythonsimplified]]
+ * [[https://stackoverflow.com/questions/55347581/why-does-the-is-operator-behave-differently-in-a-script-vs-the-repl][Why does the `is` operator behave differently in a script vs the REPL? - Stack-Overflow]]