When data is passed from Python to a native library (such as in an O/S call), how does the unboxing of data types occur? For a specific instance, os.open allows an integer whose various bits express desired behavior as `flags` -- if flags is 1, for example, the file is open write-only. If I pass an int-like object to os.open, __int__ is called; if I pass a thin wrapper over int to os.open, __int__ is not called. So the real question: anywhere in Python where an int is expected (for lower-level API work), but not directly received, should __int__ (or __index__) be called? and failure to do so is a bug? Here's my simple test code: class Wrap: def __init__(self, value): self.value = value def __int__(self): print('__int__') return self.value def __index__(self): print('__index__') return self.value class Thin(int): def __int__(self): print('__int__') return super().__int__() def __index__(self): print('__index__') return super().__index__() two = Wrap(2) [0, 1, 2][two] # __index__ # 2 import struct struct.pack('i', two) # __index__ # b'\x02\x00\x00\x00' t = Thin(1) huh = os.open('blah.txt', t) # Traceback (most recent call last): # File "<stdin>", line 1, in <module> # FileNotFoundError: [Errno 2] No such file or directory: 'blah.txt' -- ~Ethan~