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20220528104202-set_et_frozenset.org

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+:PROPERTIES:
+:ID:       cc0e3fd0-2832-4bf6-909f-354507f7ed11
+:mtime:    20220528110155
+:ctime:    20220528104202
+:END:
+#+title: Set et frozenset
+
+* /Set/
+Un /set/ est un ensemble /mutable/ et non ordonné d'éléments uniques.
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+print(f'{groceries = }')
+#+END_SRC
+
+#+RESULTS:
+: groceries = {'milk', 'chocolate', 'cheese'}
+
+** Egalité
+L'ordre n'a pas d'impact sur l'égalité entre deux /set/ :
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+print(f'{set(["milk", "cheese", "chocolate"])==set(["chocolate", "milk", "cheese"]) = }')
+#+END_SRC
+
+#+RESULTS:
+: set(["milk", "cheese", "chocolate"])==set(["chocolate", "milk", "cheese"]) = True
+
+** /Set comprehension/
+#+BEGIN_SRC python :results output
+veggies = ["broccoli", "carrot", "tomato", "pepper", "lettuce"]
+veggies_with_c = {veggie for veggie in veggies if "c" in veggie}
+
+print(f'{veggies = }')
+print(f'{veggies_with_c = }')
+#+END_SRC
+
+#+RESULTS:
+: veggies = ['broccoli', 'carrot', 'tomato', 'pepper', 'lettuce']
+: veggies_with_c = {'carrot', 'lettuce', 'broccoli'}
+
+** Opérations sur les /set/
+*** L'intersection entre des /set/ est réalisée avec l'opérateur ~&~
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+treats = {"chocolate", "popcorn", "cookie"}
+
+print(f'{groceries & treats = }')
+#+END_SRC
+
+#+RESULTS:
+: groceries & treats = {'chocolate'}
+
+*** L'union entre des /set/ est réalisée avec l'opérateur ~|~
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+treats = {"chocolate", "popcorn", "cookie"}
+
+print(f'{groceries | treats = }')
+#+END_SRC
+
+#+results:
+: groceries | treats = {'cheese', 'popcorn', 'chocolate', 'milk', 'cookie'}
+
+*** La différences entre /set/ est réalisée avec l'opérateur ~-~
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+treats = {"chocolate", "popcorn", "cookie"}
+
+print(f'{groceries - treats = }')
+#+END_SRC
+
+#+RESULTS:
+: groceries - treats = {'milk', 'cheese'}
+
+* /Frozenset/
+A l'inverse du /set/, le /frozenset/ est /immutable/ et est donc /hashable/ (utilisable comme clé des /dict/).
+
+#+BEGIN_SRC python :results output
+groceries = {"milk", "cheese", "chocolate"}
+frozen_groceries = frozenset(groceries)
+
+try:
+    frozen_groceries.add("beans")
+except AttributeError as e:
+    print(e)
+
+d = {}
+
+try:
+    d[groceries] = None
+except TypeError as e:
+    print(e)
+
+d[frozen_groceries] = None
+print(f'{d = }')
+#+END_SRC
+
+#+RESULTS:
+: 'frozenset' object has no attribute 'add'
+: unhashable type: 'set'
+: d = {frozenset({'chocolate', 'milk', 'cheese'}): None}
+
+
+
+* Références
+ * [[https://mathspp.com/blog/pydonts/set-and-frozenset][Set and frozenset - Pydon't]]