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copied!<p>The documentation for these is at <a href="http://docs.python.org/3.0/c-api/typeobj.html" rel="noreferrer">http://docs.python.org/3.0/c-api/typeobj.html</a> and <a href="http://docs.python.org/3.0/extending/newtypes.html" rel="noreferrer">http://docs.python.org/3.0/extending/newtypes.html</a> describes how to make your own type.</p> <p>tp_alloc does the low-level memory allocation for the instance. This is equivalent to malloc(), plus initialize the refcnt to 1. Python has it's own allocator, PyType_GenericAlloc, but a type can implement a specialized allocator.</p> <p>tp_new is the same as Python's __new__. It's usually used for immutable objects where the data is stored in the instance itself, as compared to a pointer to data. For example, strings and tuples store their data in the instance, instead of using a char * or a PyTuple *.</p> <p>For this case, tp_new figures out how much memory is needed, based on the input parameters, and calls tp_alloc to get the memory, then initializes the essential fields. tp_new does not need to call tp_alloc. It can for example return a cached object.</p> <p>tp_init is the same as Python's __init__. Most of your initialization should be in this function.</p> <p>The distinction between __new__ and __init__ is called <a href="http://groups.google.com/group/comp.lang.python/msg/e78840758484b94d" rel="noreferrer">two-stage initialization</a>, or <a href="http://groups.google.com/group/comp.lang.python/browse_thread/thread/b129dc656f4d0c8b/e43ae56909c3c00a?lnk=gst&q=two-phase+init#e43ae56909c3c00a" rel="noreferrer">two-phase initialization</a>. </p> <p>You say "<em>c++ just has new</em>" but that's not correct. tp_alloc corresponds a custom arena allocator in C++, __new__ corresponds to a custom type allocator (a factory function), and __init__ is more like the constructor. That last link discusses more about the parallels between C++ and Python style.</p> <p>Also read <a href="http://www.python.org/download/releases/2.2/descrintro/" rel="noreferrer">http://www.python.org/download/releases/2.2/descrintro/</a> for details about how __new__ and __init__ interact.</p> <p>You write that you want to "create the object directly in c++". That's rather difficult because at the least you'll have to convert any Python exceptions that occurred during object instantiation into a C++ exception. You might try looking at Boost::Python for some help with this task. Or you can use a two-phase initialization. ;)</p>

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