Set (ensemble)

Un set est une collection non ordonnée et non indexée. On ne peut pas modifier un item, mais on peut en ajouter.

Créer un set:

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set
{'alpha', 'beta', 'gamma'}
>>> type(un_set)
<class 'set'>

>>> autre_set = {"alpha", "beta", "gamma", "beta", "alpha"}
>>> len(autre_set)
3
>>> autre_set
{'beta', 'alpha', 'gamma'}

# Constructor set()
>>> un_set = set(("alpha", "beta", "gamma"))
>>> un_set
{'gamma', 'alpha', 'beta'}

Ajouter un item:

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.add("delta")
>>> un_set
{'gamma', 'alpha', 'beta', 'delta'}

Ajouter plusieurs items:

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.update(["delta","zeta","epsilon"])
>>> un_set
{'zeta', 'alpha', 'beta', 'delta', 'gamma', 'epsilon'}

Longueur d'un set:

>>> un_set = {"alpha", "beta", "gamma"}
>>> print(len(un_set))
3

Supprimer un item (remove):

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.remove("beta")
>>> un_set
{'gamma', 'alpha'}

# Si on retire un élément qui n'existe pas => Erreur
>>> un_set.remove("delta")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'delta'

Supprimer un item (discard):

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.discard("beta")
>>> un_set
{'gamma', 'alpha'}

# Si on retire un élément qui n'existe pas.
>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.discard("delta")
>>> un_set
{'alpha', 'gamma', 'beta'}

Vider un set:

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set.clear()
>>> un_set
set()

Supprimer un set:

>>> del un_set
>>> un_set
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'un_set' is not defined

Boucle:

un_set = {"alpha", "beta", "gamma"}
for x in un_set:
    print(x)

alpha
beta
gamma

Test si un item est présent dans le set:

un_set = {"alpha", "beta", "gamma"}
print("alpha" in un_set)

True

Set => pas d'indice:

>>> un_set = {"alpha", "beta", "gamma"}
>>> un_set[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'set' object does not support indexing

Opérateurs:

• a | b (union),
• a & b (intersection),
• a - b (différence),
• a ^ b (différence symétrique)

Méthodes:

Méthodes	Description
add()
clear()
copy()
difference()
difference_update()
discard()
intersection()
intersection_update()
isdisjoint()
issubset()
issuperset()
pop()
remove()
symmetric_difference()
symmetric_difference_update()
union()
update()

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Dernière mise à jour: May 12, 2019