Why Python Is Slow: Looking Under the Hood

Re:Why Python Is Slow: Looking Under the Hood by dragonwriter on Tuesday November 18, 2014 @07:08PM (#8627280)

> The compiler should be able sift through the code and see that "x=1" is an integer, or converts to a float when "x=x+1.0".

The short version is "no, it shouldn't".

The longer version is that, viewing Python's runtime class memberships as "types", the type system it would represent is not one for which inference without explicit declarations is generally decidable, so an AOT compiler for unmodified, unrestricted Python that is expected to infer types at runtime simply would not be possible.

You could AOT compile it into C code with a lot of runtime metadata and indirections -- but that would probably have worse performance than the existing interpreter.

> Way back when, you could get a BASIC compiler to turn your interpreted BASIC code into assembly.

Well, yeah, BASIC is actually structurally quite close to assembly. Its not a dynamically-typed multiparadigm language like Python.

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Re:Why Python Is Slow: Looking Under the Hood by JoeAltmaier on Tuesday November 18, 2014 @07:11PM (#8627297)

Its hard to be worse than an interpreter. 100X slower than compiled code is typical. Whatever 'metadata and indirection' your C target has, it seems likely to be 10X better than interpreted, easily.

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Re:Why Python Is Slow: Looking Under the Hood by dagw on Wednesday November 19, 2014 @03:43AM (#8628912)

Cython is a very mature python-to-C translator and it offers 0-40% speed improvements in my experience on straight Python. To get any significant speedups you have to add type declarations, replace python function with equivalent C functions from the standard library, turn off bounds checking and bunch of similar things. But if you do that then it does produce some pretty fast code.

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Re:Why Python Is Slow: Looking Under the Hood by dragonwriter on Tuesday November 18, 2014 @07:30PM (#8627400)

> Its hard to be worse than an interpreter.

Its actually quite easy to be worse than an interpreter that is actually a combination of a bytecode compiler and a VM built around the execution model of the language it is for, which is what the main Python interpreter is.

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Re:Why Python Is Slow: Looking Under the Hood by JoeAltmaier on Wednesday November 19, 2014 @10:42AM (#8630584)

Interpreters have to be implemented somehow; that's a way. Its not fast. Its orders of magnitude slower than native code. Even bad native code.

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