递归在 python（递归的源代码）内部如何工作？

Question

I would like to understand the internal work of recursion. Can I write my own recursion for python?

For example, now we have following function:

def fact(n):
    return n*fact(n)

How can I change the return command and change the functionality of it, like the following:

def fact(n):
    my_return  n*fact(n)

In this case, I want to change the internal work of return and use my_returne, and also with this, I want to control stack differently.

Answer 1

If you want to understand the guts of how Python works, I highly recommend reading the documentation for the built-in modules under the "Language Services" heading, particularly the ast and dis modules. Python exposes, as importable and Python-runnable modules, all of its parsing capabilities. You can see, use, and tinker with its parsing of code, how it generates bytecode, and its core execution.

I'm not sure if this really helps, but RETURN_VALUE is its own opcode in Python's bytecode, so aside from creating your own bytecode manually or screwing with the parser results, there's probably no other way to get the return keyword's behavior. The actual implementation of how that behaves is going to be implementation-dependent (CPython might do it differently from Pypy, for example), so you'd need to be more specific in your question, or just dig into their source code for that opcode.

That said, there's nothing stopping you from creating your own stack as a list and pushing/popping stack frames to/from it yourself, besides the sheer insanity of the act. Eg,

stack = []

def my_pseudo_func():
    global stack
    args, kwargs = stack[-1]
    x, = args
    # do some stuff
    my_return_result = x + 5
    ###
    stack.pop()
    stack.append(my_return_result)

stack.append(((3,), {}))
my_pseudo_func()
result = stack.pop()
assert result == 8