Removed an outdated pxd, added a declaration of exc.pxd and made two examples for exceptions.

Cython/Includes/cpython/exc.pxd

@@ -153,6 +153,13 @@ cdef extern from "Python.h":
     # PyErr_SetFromErrno(type);" when the system call returns an
     # error.
 
+    PyObject* PyErr_SetFromErrnoWithFilenameObject(object type, object filenameObject) except NULL
+    # Similar to PyErr_SetFromErrno(), with the additional behavior
+    # that if filenameObject is not NULL, it is passed to the
+    # constructor of type as a third parameter.
+    # In the case of OSError exception, this is used to define
+    # the filename attribute of the exception instance.
+
     PyObject* PyErr_SetFromErrnoWithFilename(object type, char *filename) except NULL
     # Return value: Always NULL.  Similar to PyErr_SetFromErrno(),
     # with the additional behavior that if filename is not NULL, it is

docs/examples/tutorial/external/keyword_args_call.pyx

@@ -4,4 +4,4 @@ cdef extern from "string.h":
 cdef char* data = "hfvcakdfagbcffvschvxcdfgccbcfhvgcsnfxjh"
 
 cdef char* pos = strstr(needle='akd', haystack=data)
-print(pos != NULL)
+print(pos is not NULL)

docs/examples/userguide/language_basics/open_file.pyx

 from libc.stdio cimport FILE, fopen
+from libc.stdlib cimport malloc, free
+from cpython.exc cimport PyErr_SetFromErrnoWithFilenameObject
 
-
-def main():
+def open_file():
     cdef FILE* p
     p = fopen("spam.txt", "r")
-    if p == NULL:
-        raise OSError("Couldn't open the spam file")
-    # ...
+    if p is NULL:
+        PyErr_SetFromErrnoWithFilenameObject(OSError, "spam.txt")
+    ...
+
+
+def allocating_memory(number=10):
+    cdef double *my_array = <double *> malloc(number * sizeof(double))
+    if not my_array:
+        raise MemoryError()
+    ...
+    free(my_array)

docs/src/userguide/extension_types.rst

@@ -419,7 +419,7 @@ compatible types.::
         cdef void* ptr
 
         def __dealloc__(self):
-            if self.ptr != NULL:
+            if self.ptr is not NULL:
                 free(self.ptr)
 
         @staticmethod

docs/src/userguide/parallelism.rst

@@ -131,7 +131,7 @@ It currently supports OpenMP, but later on more backends might be supported.
 
        with nogil, parallel():
            local_buf = <int *> malloc(sizeof(int) * size)
-           if local_buf == NULL:
+           if local_buf is NULL:
                abort()
 
            # populate our local buffer in a sequential loop