Tim Delaney <timothy.c.dela...@gmail.com> writes: [...] > As others have said, typing is about how the underlying memory is treated.
No. It is much more than that. Typing is about everything you can say about a given statement. Some type systems are focusing on type labels only (like most statically typed programming languages), others are fairly elaborate (for instance, Eiffel's, if requires/ensures are considered part of the type system). There is a wide range of type systems, more or less practical depending on your needs (see https://www.cis.upenn.edu/~bcpierce/tapl/ if you want to see how far you can go with typing). [...] > C is statically and weakly typed. Variables know their types at compile > time (static typing). It is a feature of the language that you can cast any > pointer to any chunk of memory to be a pointer to any other type (normally > via void *). This is not coercion - it takes the bit pattern of memory of > one type and interprets it as the bit pattern for another type, and is weak > typing. No. C has much stronger rules, not on casting, but on accessing the pointees, which basically invalidates your argument. Refer to the C standard for details. > Python is strongly and dynamically typed. In Python, once you create an > object, it remains that type of object, no matter what you do to it*. That > makes it strongly typed. [...] But you can modify the class (not __class__) in whatever way you want. For instance: class X(object): def f(self): ... ... del X.f So, in Python, knowing that object x is an instance of class X tells you... essentially nothing. Call this strong typing if you want. In terms of type systems, it is (strong) simplistic-typing based on type labels, and labels carry no information whatsoever. Dynamic typing lets you avoid doing nonsense with bit-patterns, as you say, by gracefully crashing at run-time instead of performing "unexpected" actions. "Unexpected" is defined by the whole *execution* of the program up to the point where typing takes place. To understand whether a Python statement x.f() is meaningful (which is what typing is about), you have to know the full sequence of actions that have taken place on x *and* on its class (and on everything that that call may use) since the beginning of the program. For any non-trivial program, this is usually way too complex to capture, testing will be incomplete, and all you can do is run your program and see whether is goes through. As a general rule, if that's all you expect from typing, then, fine, call this "strong". I won't go as far, and just say that it is good enough for the programs I use Python for. -- Alain. -- https://mail.python.org/mailman/listinfo/python-list
