> #cython: boundscheck = False
> #cython: wraparound = False
> import numpy as np
> import time
> cdef class Mem_slice(object):
>     cdef double[::1] x
>     def __init__(self, x):
>         self.x=x

> cdef int i
> a=np.ones(10000000,"f8")
> cdef Mem_slice m=Mem_slice(a)

> #[1] the most convenient way but the slowest. time: 1.30s
> t1=time.clock()
> for i in range(10000000):
>     m.x[i]=2.0
> t2=time.clock()
> print t2-t1

> #[2] the fastest way. time: 0.034s
> t1=time.clock()
> cdef double[::1] x=m.x
> for i in range(10000000):
>     x[i]=2.0
> t2=time.clock()
> print t2-t1

> #[3] directly use numpy array index. time: 1.17s
> t1=time.clock()
> for i in range(10000000):
>     a[i]=2.0
> t2=time.clock()
> print t2-t1

> I dig a little bit the generated C source then I find:

>     /* "mtest.pyx":17
>  * t1=time.clock()
>  * for i in range(10000000):
>  *     m.x[i]=2.0             # <<<<<<<<<<<<<<
>  * t2=time.clock()
>  * print t2-t1
>  */
>     if (unlikely(!__pyx_v_5mtest_m->x.memview))
> {PyErr_SetString(PyExc_AttributeError,"Memoryview is not
> initialized");{__pyx_filename = __pyx_f[0]; __pyx_lineno = 17; __pyx_clineno
> = __LINE__; goto __pyx_L1_error;}}
>     __pyx_t_4 = __pyx_v_5mtest_m->x; // here is the second time consuming
> part due to the memoryview slice object's assign(copy) to temporary
> variable.
>    //Here is the most time consuming part because of the
> PyThread_acquire_lock and PyThread_release_lock (in __PYX_INC_MEMVIEW
> and __PYX_XDEC_MEMVIEW  )
>     __PYX_INC_MEMVIEW(&__pyx_t_4, 1);
>     __pyx_t_5 = __pyx_v_5mtest_i;
>     *((double *) ( /* dim=0 */ ((char *) (((double *) __pyx_t_4.data) +
> __pyx_t_5)) )) = 2.0;
>     __PYX_XDEC_MEMVIEW(&__pyx_t_4, 1);

> since I am not writing parallel code so may be there's no need to acquire
> the lock.
> (maybe add a Compiler directives to enble or unable this?)
> Maybe it can use the pointer to avoid the copy overhead or put the assign
> opereration ( __pyx_t_4 = __pyx_v_5mtest_m->x;) outside the loop

> I didn't familiar with python's thread or compiler optimization, it would be
> my honor to be pointed out.

> Best Regards,
> liu zhenhai