Added some info about is and ==

ex_01_03.py

@@ -12,3 +12,14 @@ def bailey_borwein_plouffe_pi(n):
 if( __name__ == "__main__"):
 
 	assert bailey_borwein_plouffe_pi(1000) == math.pi
+
+	# Please note that the ``is`` operator checks wether the
+	# two references are the same object, basically by comparing
+	# their pointers.
+	#
+	# The ``==`` operator accesses the ``__eq__`` method of the 
+	# object that *compares* the other object to itself.
+	#
+	# Because ``a/b`` **cannot** return the same object as ``math.pi``,
+	# the latter was created when the module ``math`` was initialized,
+	# this will **always** evaluate to False.