How to get function code object from bytecode?

Question

I need to create a call graph of python function and then modify bytecode of some functions.

I started to play with disassembly and found that function is make by MAKE_FUNCTION opcode and the code object somehow passed to it

 32          96 LOAD_CONST              25 ((None, None, True, 'off', None, False))
             98 LOAD_CONST              15 (<code object foobar at 0x7fc46bff6d20, file "foo.py", line 25>)
            100 LOAD_CONST              16 ('foo')
            102 MAKE_FUNCTION            1
            104 STORE_NAME              15 ('fun')

Okay, I found roots of the callgraph in this file, but what to do next? How do I actually get this code object?

kindall · Accepted Answer · 2017-10-03 18:43:23Z

1

The function type is what you want. You can get it from the types module (where it is types.FunctionType) or just type(lambda:0). Do a help() on the type to see the arguments required to create a function object.

The primary thing you need to construct the function is the code object. You can get that from an existing function f using f.func_code. If you are modifying the bytecode you will need to create a new code object to contain it. Its type can be obtained using type() as with the function and doing a help() on the type will tell you what you need to pass in.

If you are basing the new function on an existing one, then you can dig most of what you need out of the existing function. See this table in the inspect module documentation to see what attributes of functions and code objects contain things of interest to you.

answered Oct 3, 2017 at 18:43

kindall

185k36 gold badges291 silver badges321 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

user1685095 Over a year ago

Um... I don't see how this answers my question. I have a pyc file, I've disassembled it with dis.dis. Then what?

kindall Over a year ago

So you have the function, or you couldn't have disassembled it with dis. So the code object of function f is f.func_code and the bytecode string is f.func_code.co_code. You say you want to modify the bytecode, and once you do that you will need to build a new function from it, which you can do using the code and function types.

user1685095 Over a year ago

What if I don't have source files and have only compiled files?

user1685095 Over a year ago

Okay, it's in co_consts

Collectives™ on Stack Overflow

How to get function code object from bytecode?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related