Check signature of handler

[ttmetro]

How do I check the signature of a function?

I define it in Python

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def handler_function(arg1, arg2):
    pass

and then call it with the following C code:

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mp_call_function_2(handler_function, arg1, arg2)

This works well, but crashes the VM if the handler function is not declared with the correct signature (two arguments).

How can I verify the handler signature in C (i.e. that it takes exactly two arguments)?

Presently I just check that it's a function:

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    if (MP_OBJ_IS_FUN(handler_obj) || MP_OBJ_IS_METH(handler_obj)) {
        stdout_handler = handler_obj;
    } else {
        mp_raise_ValueError("function expected");
    }

[jimmo]

Hi,

When I do this in C (inside a function callable from Python taking a single argument).

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mp_call_function_2(obj, mp_const_none, mp_const_none);

where obj was the argument passed into the function.

Then from the REPL:

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>>> def bar():
...     print('bar')
...    
>>> my_c_function(bar)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bar() takes 0 positional arguments but 2 were given
>>> 

So it's unexpected that you're seeing a VM crash...?

To answer your question though -- it isn't easy to answer the question "how many params does a function take".

For example:

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def handler_function(*args):
  pass

Internally in the VM, the signature is represented differently depending on how it was defined (i.e. C, inline asm, regular bytecode, etc). The way this is implemented, it's the responsibility of the callee to figure out if it has been given the right number of arguments. Look at fun_builtin_var_call and fun_bc_call for more information for two of those cases.

[ttmetro]

Thanks. What I actually did is forward everything that's written to stdout to the handler. The exception prints the error message - and results in an infinite loop.

Confused myself; should have tried a simpler example (like what I posted).