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- python - Why do some functions have underscores - Stack Overflow
The other respondents are correct in describing the double leading and trailing underscores as a naming convention for "special" or "magic" methods While you can call these methods directly ([10, 20] __len__() for example), the presence of the underscores is a hint that these methods are intended to be invoked indirectly (len([10, 20]) for example) Most python operators have an associated
- TypeError: type object is not subscriptable in a function signature
The following answer only applies to Python < 3 9 The expression list[int] is attempting to subscript the object list, which is a class Class objects are of the type of their metaclass, which is type in this case Since type does not define a __getitem__ method, you can't do list[ ] To do this correctly, you need to import typing List and use that instead of the built-in list in your type
- oop - What do __init__ and self do in Python? - Stack Overflow
In this code: class A(object): def __init__(self): self x = 'Hello' def method_a(self, foo): print self x + ' ' + foo the self variable represents the instance of the object itself Most object-oriented languages pass this as a hidden parameter to the methods defined on an object; Python does not You have to declare it explicitly When you create an instance of the A class and call its
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