Rafael Almeida wrote:
> I'm studying compilers now on my university and I can't quite
> understand one thing about the python interpreter. Why is its input a
> binary file (pyc)? The LOAD_CONST opcode is 100 (dec) and STORE_FAST's
> is 125 (dec). The translation of the following code:
>
> foo.py:
> x = 10
>
> Could be this:
>
> foo.pyc:
> 100 10
> 125 0
>
> That way you wouldn't need code such as
> static void
> w_long(long x, WFILE *p)
> {
> w_byte((char)( x & 0xff), p);
> w_byte((char)((x>> 8) & 0xff), p);
> w_byte((char)((x>>16) & 0xff), p);
> w_byte((char)((x>>24) & 0xff), p);
> }
> since you could read it with strtol and write back using a simple
> printf. So you wouldn't need a buch of casts by simple using ascii
> input and output.
A "simple" printf or strtol involves hundreds of instructions. And
people want Python to execute fast...
> What's the reason for having it in a binary form instead of writting
> it in ascii? (yeah, I know ascii would be binary also, but I think you
> get my point.)
Speed? Eficiency? File size? Ease of use?
A .pyc *could* be written in ASCII, but what do you gain? Replacing a
few trivial functions in the Python core with a printf/scanf equivalent?
At the same time you lose a lot of speed, so I don't see the point.
> So I was writting this interpreter for some assembly language defined
> in class and I did something like python does, so I had a binary file
> to interpret. After a while I thought it was far harder to program.
Why harder? Once you read the file, they're just numbers. Anyway, being
harder to program the *interpreter* is not a problem, if you gain
something like speed or eficiency for the interpreted language.
> And when I tried to code an assembler my problems got greater, as I
> wanted to code it in python (the interpreter was in C++) and I had a
> hard time trying to figure out how I would print something that's not a
> ascii or unicode string. As for the benefits, I couldn't figure out any.
Sorry, I could not understand what you said here.
--
Gabriel Genellina
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