Put the nonecheck example in a separate file in the examples directory to enable testing.

docs/examples/tutorial/cdef_classes/nonecheck.pyx

+# cython: nonecheck=True
+#        ^^^ Turns on nonecheck globally
+
+import cython
+
+cdef class MyClass:
+    pass
+
+# Turn off nonecheck locally for the function
+@cython.nonecheck(False)
+def func():
+    cdef MyClass obj = None
+    try:
+        # Turn nonecheck on again for a block
+        with cython.nonecheck(True):
+            print obj.myfunc()  # Raises exception
+    except AttributeError:
+        pass
+    print(obj.myfunc())  # Hope for a crash!

docs/src/tutorial/cdef_classes.rst

@@ -103,26 +103,9 @@ Some notes on our new implementation of ``evaluate``:
 
 There is a *compiler directive* ``nonecheck`` which turns on checks
 for this, at the cost of decreased speed. Here's how compiler directives
-are used to dynamically switch on or off ``nonecheck``::
-
-  #cython: nonecheck=True
-  #        ^^^ Turns on nonecheck globally
-
-  import cython
-
-  # Turn off nonecheck locally for the function
-  @cython.nonecheck(False)
-  def func():
-      cdef MyClass obj = None
-      try:
-          # Turn nonecheck on again for a block
-          with cython.nonecheck(True):
-              print obj.myfunc() # Raises exception
-      except AttributeError:
-          pass
-      print obj.myfunc() # Hope for a crash!
-
+are used to dynamically switch on or off ``nonecheck``:
 
+.. literalinclude:: ../../examples/tutorial/cdef_classes/nonecheck.pyx
 
 Attributes in cdef classes behave differently from attributes in regular classes: