python - Is it at all possible to create indirectly recursive ctypes.Structure types? -

this not same #1228158 or #28879604. it's similar, twist.

it's trivial create recursive type referring own type:

a = type('a', (ctypes.structure,), {}) a._fields_ = [('another_a', ctypes.pointer(a))] 

or, if prefer:

class a(ctypes.structure):     pass a._fields_ = [('another_a', ctypes.pointer(a))] 

same thing. if they're not same thing, educate me!

but i'm trying machine-translate c structs , typedefs ctypes.structures. want names , relations on python side reflect on c side. if function returning uint32 typedefed consumer_id, want object on python side have more descriptive name. now, here's type of thing occurs quite often:

typedef dummy_type official_type; typedef struct dummy_struct {     official_type *another_struct; } dummy_type; 

no matter how twist , turn this, can't realize relation in python. intermediate names probably not used anywhere, @ moment we're going idea of detecting situation , making official_type ctypes.structure referring itself. , maybe make dummy_type , struct dummy_struct types referring themselves. on binary level, on c side, they'll equivalent.

but want this:

struct_dummy_struct = type('struct_dummy_struct', (ctypes.structure,), {}) dummy_type = type('dummy_type', (struct_dummy_struct,), {}) official_type = type('official_type', (dummy_type,), {}) struct_dummy_struct._fields_ = [('another_struct', ctypes.pointer(official_type))] 

of course, not possible:

traceback (most recent call last):   file "<stdin>", line 1, in <module> attributeerror: _fields_ final 

i think i'm trying theoretically impossible, given way ctypes works, if tell me there's way, delighted!

you not need same construction in python:

class official_type(ctypes.structure):     pass official_type._fields_ = [("another_struct", ctypes.pointer(official_type))] first_instance = official_type() second_instance = official_type() first_instance.another_struct = ctypes.pointer(second_instance) print first_instance.another_struct 

<__main__.lp_official_type object @ ...>

ctypes has funky struct finalization process, if dig unit tests you'll find like:

structure/union classes must 'finalized' sooner or later, when 1 of these things happen:

1. _fields_ set.
2. an instance created.
3. the type used field of structure/union.
4. the type subclassed

when finalized, assigning fields no longer allowed.

perhaps class definition using type messes process up.