I just realized the Python does not provide a fast way of popping an
item from a list, just append. I.e. there is a PyList_Append, but no
PyList_Pop. And in Python's code for _listobject.c, the function listpop
is declared static. When using a list as a stack (a common case for
Python lists), a fast pop is just as important as a fast append.
Since the function listpop is static, the fastest way to pop a list is
to grab the method named "pop" from the PyTypeObject. This might not be
obvious to everyone, so I think it is an optimization that Cython should do.
Sturla Molden
cdef extern from "Python.h":
ctypedef object (*PyCFunction)(object self, object args)
ctypedef struct PyMethodDef:
char *ml_name
PyCFunction ml_meth
ctypedef struct PyTypeObject:
PyMethodDef *tp_methods
PyTypeObject PyList_Type
cdef PyCFunction __listpop = NULL
cpdef listpop(list self, Py_ssize_t n=-1):
global __listpop
cdef PyMethodDef *ptr
cdef int ok = 0
if not __listpop:
ptr = PyList_Type.tp_methods;
while ptr:
if str(ptr[0].ml_name) == "pop":
__listpop = ptr.ml_meth
ok = 1
break
ptr += 1
if not ok:
raise ValueError, \
'Could not find method "pop" in list type object'
return __listpop(self, (int(n),))
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