Weekly backup.

20220528161514-la_methode_bool.org

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+:PROPERTIES:
+:ID:       5803422c-c089-4369-93cc-80caca71a26b
+:mtime:    20220528173751
+:ctime:    20220528161514
+:END:
+#+title: La méthode __bool__
+
+* Synthaxe
+#+BEGIN_SRC python
+object.__bool__(self)
+#+END_SRC
+La méthode ~object.__bool__~ :
+ * “Any object can be tested for truth value, for use in an if or while condition or as operand of the Boolean operations below [or, and and not].”,
+ * Un objet est /Falsy/ lorsqu'il est /empty/ ou /without any useful value/,
+ * Est appelée par la fonction /built-in/ /bool/.
+
+* Exemples
+#+BEGIN_SRC python :results output
+print(f'{bool(None) = }')
+
+print(f'{bool([]) = }')
+print(f'{bool([None]) = }')
+
+print(f'{bool({}) = }')
+
+#+END_SRC
+#+RESULTS:
+: bool(None) = False
+: bool([]) = False
+: bool([None]) = True
+: bool({}) = False
+
+ * Par défaut, les instances de classes retournent /True/ :
+#+BEGIN_SRC python :results output
+class Dummy:
+    pass
+
+print(f'{bool(Dummy()) = }')
+#+END_SRC
+#+RESULTS:
+: bool(Dummy()) = True
+
+#+BEGIN_SRC python :results output
+class Dummy:
+
+    def __bool__(self) -> bool:
+        return False
+
+print(f'{bool(Dummy()) = }')
+#+END_SRC
+#+RESULTS:
+: bool(Dummy()) = False
+
+* Références
+ * [[https://mathspp.com/blog/pydonts/truthy-falsy-and-bool][Truthy falsy and bool - Pydon't]]
+