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Python was already strongly typed long before Python 3. Python does not have static typing as a built-in part of the language. It has had the ability to annotate arguments and returns of functions/methods since 3.0, a standard-library module containing helpful code to use this for type hints since 3.5, and the ability to annotate variables since 3.6. Annotations are a completely optional feature and no built-in part of Python will check these annotations or analyze code for correctness in advance of execution; there are third-party tools to do this, if you want it. Also, Python most certainly does compile -- the CPython interpreter is a virtual machine which runs bytecode, and Python source code is compiled to bytecode for that VM. There isn't a requirement to run a completely separate standalone Python compiler ahead-of-time to generate the bytecode (if bytecode isn't available, Python will compile source to bytecode on a per-module basis as those modules are loaded), but that doesn't mean it isn't compiled. As to "strong" typing: "Strong" typing is a term that's only vaguely defined, but most commonly refers to whether a language will implicitly coerce/cast values of incompatible types in order to make an operation succeed. Consider this code: a = 1
b = "2"
c = a + b
In a strongly-typed language this is an error¹. Depending on other aspects of the language, it may be a compile-time error or it may be a runtime error, but the important thing is that the third line of that sample will never successfully execute. In a weakly-typed language, the third line could execute, and would assign a value of either 3 (if the string is coerced to number) or "12" (if the number is coerced to string). And in fact, in Python the third line above raises a runtime TypeError, since str and int are incompatible types for the "+" operator to work with.Static typing refers to a situation where both names and values have types, and where all attempts at binding must involve names and values of compatible types. For example, in Java: int a = 3;
The name "a" is declared to be of type int, and the value 3 is of type int, so the binding of the value to the name succeeds. Attempting to bind a non-int value to the name "a" would fail. In a dynamically-typed language, only values have types, and the type of a value does not restrict which names it can be bound to.You can remember this easily by considering why the name "static" is used: it's because you can perform checks of name/value types and bindings statically, without needing to run the code to determine types. In some languages (like Java) this is accomplished by requiring all names to be explicitly annotated with their types; in others the types will usually be inferred automatically from usage, with the option to annotate when desired or to resolve ambiguity. -- ¹ Yes, yes, I know someone on HN is going to suffer a terrible career-ending injury from how fast his knee jerked at that and possibly from breaking his wrists in his rush to post "Well actually there may be a type defined somewhere that's a union of string and number, so how dare you say that's an error when you don't know if someone might be using such a type!" My advice is not to be the type of person who suffers severe injuries due to such an obsessive need to nit-pick, because reasonable/charitable readers will correctly understand the example with no difficulty. |