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Licence de l’article: Free Documentation License
Tester l’existence d’une variable en Python
le jeudi 28 décembre 2006 par NoplayLorsque l’on débarque de langage plus permissif que Python comme PHP ou Perl on est surpris lorsqu’en essayant de tester l’existence d’une variable avec un simple if le programme s’arrete.
if toto:
print toto
Traceback (most recent call last):
File "./test.py", line 4, in ?
if toto:
NameError: name 'toto' is not definedEn Python on part du principe qu’il est plus facile de demander pardon que de d’obtenir la permission. En effet si vous voulez utiliser une variable, Python va devoir tester en interne si cette variable existe. Si vous testez l’existence de la variable avant le test sera effectué deux fois. Une perte de temps non ? Python lève donc des exceptions en cas de problème.
Dans le cas qui nous intéresse il suffit donc de catcher l’exception NameError.
try:
print toto
except NameError:
print "Toto n'existe pas"
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Tester l’existence d’une variable en Python
le 27 avril , par max-k:
Et si tu veux tester l’existence de l’attribut d’une instance de classe (d’un objet) :
Exemple, pour l’instance en cours :
if hasattr(self, 'toto'):
print(self.toto)
else:
print("l'attribut toto n'est pas défini")Exemple, pour un autre objet :
if hasattr(mon_objet, 'toto'):
print(mon_objet.toto)
...Tester l’existence d’une variable en Python
le 2 janvier , par David, biologeek:
Tu peux aussi faire : if ’toto’ in locals() : print toto