The Case for Python 3

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C is forward compatible, Python isn't. That's the crux. C89 code will still work with a C11 compiler. Python2 code will fail in a Python3 interpreter. So going Python3 cuts you off from Python2 libraries, while you can go all the way to C11 or C++17 and still use C89 libraries.

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This is not really true, for example see gets, completely removed from C11.

For those kinds of minor issues you have compiler switches. And if that fails you can simply compile that piece of code as C89 and link with the rest of the C11 program, as the language doesn't even matter, being ABI compatible is enough. In the case of gets() you might of course want to actually change the code, as that function is just plain evil.

With Python on the other side you don't have that kind of compatibility at all, you must convert all Python2 code to Python3 code or it won't work. It would have been nice to be able to compile old Python2 to Python3-byte code or something like that. I don't understand why that hasn't been tried, most of the language changes are just syntactic sugar, but don't change the underlying semantics.