39 lines
1.3 KiB
Org Mode
39 lines
1.3 KiB
Org Mode
:PROPERTIES:
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:ID: 24408701-21d8-4f4e-aed9-c58746df2244
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:mtime: 20220516142825
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:ctime: 20220516125736
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:END:
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#+title: Différence entre les opérateurs + et +=
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* Introduction
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Comment expliquer la différence de comportement entre les opérateurs *+* et *+=* :
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#+BEGIN_SRC python :results output
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a1 = a2 = [1, 2]
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a1 += [3] # Uses __iadd__, modifies a1 in-place
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print(f"When += is used: {a1=}, {a2=}")
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a1 = a2 = [1, 2]
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a1.extend([3]) # Uses __add__, creates new list, assigns it to b1
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print(f"When extend is used: {a1=}, {a2=}")
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a1 = a2 = [1, 2]
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a1 = a1 + [3] # Uses __add__, creates new list, assigns it to b1
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print(f"When + is used: {a1=}, {a2=}")
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#+END_SRC
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#+RESULTS:
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: When += is used: a1=[1, 2, 3], a2=[1, 2, 3]
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: When extend is used: a1=[1, 2, 3], a2=[1, 2, 3]
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: When + is used: a1=[1, 2, 3], a2=[1, 2]
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* Explications
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L'opérateur *+=* appelle la méthode dunder *__iadd__*. Si celle-ci n'existe pas (cas des objets /immutables/), il
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appelle *__add__*:
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* La méthode *__iadd__* signifie *in-place addition* : cela implique la modification de l'objet /mutable/ (et non la création
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d'une nouvelle instance - cf. __add__),
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* La méthode *__add__* retourne un nouvel object contenant le résultat de l'opération.
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* Références
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* [[https://stackoverflow.com/questions/2347265/why-does-behave-unexpectedly-on-lists/2347423#2347423][Stackoverflow]]
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