Most Python/C API functions have one or more arguments as well as a
return value of type PyObject*. This type is a pointer
to an opaque data type representing an arbitrary Python
object. Since all Python object types are treated the same way by the
Python language in most situations (e.g., assignments, scope rules,
and argument passing), it is only fitting that they should be
represented by a single C type. Almost all Python objects live on the
heap: you never declare an automatic or static variable of type
PyObject, only pointer variables of type PyObject* can
be declared. The sole exception are the type objects;
since these must never be deallocated, they are typically static
PyTypeObject objects.
All Python objects (even Python integers) have a type and a
reference count. An object's type determines what kind of object
it is (e.g., an integer, a list, or a user-defined function; there are
many more as explained in the Python
Reference Manual). For each of the well-known types there is a macro
to check whether an object is of that type; for instance,
"PyList_Check(a)" is true if (and only if) the object
pointed to by a is a Python list.
