#cython: language_level=3

"""

This module provides mixin bases classes for the Column and MaskedColumn

classes to provide those classes with their custom __getitem__ implementations.

The reason for this is that implementing a __getitem__ in pure Python actually

significantly slows down the array subscript operation, especially if it needs

to call the subclass's __getitem__ (i.e. ndarray.__getitem__ in this case). By

providing __getitem__ through a base type implemented in C, the __getitem__

implementation will go straight into the class's tp_as_mapping->mp_subscript

slot, rather than going through a class __dict__ and calling a pure Python

method. Furthermore, the C implementation of __getitem__ can easily directly

call the base class's implementation (as seen in _ColumnGetitemShim, which

directly calls to ndarray->tp_as_mapping->mp_subscript).

The main reason for overriding __getitem__ in the Column class is for

returning elements out of a multi-dimensional column. That is, if the

elements of a Column are themselves arrays, the default ndarray.__getitem__

applies the subclass to those arrays, so they are returned as Column instances

(when really they're just an array that was in a Column). This overrides that

behavior in the case where the element returned from a single row of the

Column is itself an array.

"""

import sys

import numpy as np

cimport numpy as np

from cpython.ref cimport PyTypeObject

np.import_array()

cdef tuple INTEGER_TYPES = (int, np.integer)

cdef tuple STRING_TYPES = (str, np.str_)

# Annoying boilerplate that we shouldn't have to write; Cython should

# have this built in (some versions do, but the ctypedefs are still lacking,

# or what is available is Cython version dependent)

ctypedef object (*binaryfunc)(object, object)

cdef extern from "Python.h":

void *PyType_GetSlot(PyTypeObject *type, int slot)

int Py_mp_subscript

ctypedef object (*item_getter)(object, object)

cdef inline object base_getitem(object self, object item, item_getter getitem):

if (<np.ndarray>self).ndim > 1 and isinstance(item, INTEGER_TYPES):

return self.data[item]

dtype_kind = (<np.ndarray>self).dtype.kind

if dtype_kind == 'V' and isinstance(item, STRING_TYPES):

return self.data[item]

value = getitem(self, item)

try:

if dtype_kind == 'S' and not value.shape:

value = value.decode('utf-8', errors='replace')

except AttributeError:

pass

return value

cdef inline object column_getitem(object self, object item):

return (<binaryfunc>PyType_GetSlot(<PyTypeObject *>np.ndarray, Py_mp_subscript))(self, item)

cdef class _ColumnGetitemShim:

def __getitem__(self, item):

return base_getitem(self, item, column_getitem)

MaskedArray = np.ma.MaskedArray

cdef inline object masked_column_getitem(object self, object item):

value = MaskedArray.__getitem__(self, item)

return self._copy_attrs_slice(value)

cdef class _MaskedColumnGetitemShim(_ColumnGetitemShim):

def __getitem__(self, item):

return base_getitem(self, item, masked_column_getitem)