Dive into CPython Bytecode

Dive into CPython Bytecode

Alex Gaynor

I don't need to know that stuff

You don't. But it's totally helpful.

How does CPython Make Bytecode?

Tokenize the source

Parse the tokens into an AST

Build a symbol table to figure out what's a global

Compile to bytecode

Now I can haz bytecode

Now that I has a bytecode how does I see it?

>>> def f(o):... return o

>>> import dis>>> dis.dis(f) 2 0 LOAD_FAST 0 (o) 3 RETURN_VALUE

So use the dis module

So now that we have bytecode, what do we do with it?

Well, what are those bytecodes?

A few examples

UNARY_NEGATIVE: -TOS

BINARY_ADD: TOS1 + TOS

SLICE+3: TOS2[TOS1:TOS]

UNPACK_SEQUENCE

LOAD_CONST

CALL_FUNCTION_VAR_KW

Python VM is stack based

So now we know some bytecodes, what can we do with this knowledge

A tale of 2 functions

>>> def f():

... return [x for x in xrange(10)]

>>> def g():

... o = []

... for x in xrange(10):

... o.append(x)

... return o

Less Bytecode == faster!

More specialized bytecodes == faster

@alex_gaynor

Thanks

09/10/09

09/10/09