#!/usr/bin/env python

list = [1, 'a', 'b', 'c', 4]
for item in list:
    print "list before: %s" % list
    try:
        item = int(item)
    except ValueError:
        print "%s cannot be cast to int. Delete it." % item
        list.remove(item)
    else:
        print "%s looks like an int. No problem, mon." % item
    print "list after : %s" % list
    print

print "### final list is %s" % list

list = [el for el in list if type(el) == int]

def convertable(x):
    try: return int(x)
    except ValueError: return None
list = [el for el in list if convertable(x) is not None]

def convertable(x):
    try: return int(x)
    except ValueError: return None
list = [int(el) for el in list if convertable(el) is not None]

static PyObject *
euler_Factors(PyObject *self, PyObject *args){

    long n, i;
    int test;
    PyObject *res;

    if(!PyArg_Parse(args,"(l)",&n))
        return NULL;

    res = PyEval_CallFunction(euler_isPrime, "i", n);

    if(!(test = PyObject_IsTrue(res)))
      return NULL;

    printf("%d\n",test);

    return res;
}

static PyObject *
euler_isPrime(PyObject *self, PyObject *args){

    unsigned long long n, i, r;

    if(!PyArg_Parse(args,"(l)",&n))
        return NULL;

    r = (unsigned long long) (sqrt((double) (n))+1.0);

    if(n<2){
      Py_RETURN_FALSE;
    }
    else{
      for(i=3;i<r;i++){
        if(n%i == 0)
          Py_RETURN_FALSE;
      }
      Py_RETURN_TRUE;
    }

}

res = PyEval_CallFunction(euler_isPrime, "i", n);

euler.c:71: warning: passing argument 1 of ‘PyEval_CallFunction’ from incompatible pointer type
/usr/include/python2.6/ceval.h:21: note: expected ‘struct PyObject *’ but argument is of type ‘struct PyObject * (*)(struct PyObject *, struct PyObject *)’

list = [int(x) for x in list if x.isdigit()]

[x for x in list if type(x) is int]