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+.. 8.4 LO: dictionaries (2)
+.. ------------------------
+.. * empty 
+.. * filled 
+.. * accessing via keys 
+.. * .values(), .keys() 
+.. * in 
+.. * iteration
+
+============
+Dictionaries
+============
+
+{{{ show the welcome slide }}}
+
+Welcome to the spoken tutorial on dictionaries.
+
+{{{ switch to next slide, outline slide }}}
+
+In this tutorial, we will see how to create empty dictionaries, learn
+about keys and values of dictionaries. Checking for elements and
+iterating over elements.
+
+{{{ switch to next slide on overview of dictionaries }}}
+
+A dictionary in general, is designed to look up meanings of
+words. Similarly, Python dictionary is also designed to look up for a
+specific key and retrieve the corresponding value. Dictionaries are
+data structures that provide key-value mappings.  Dictionaries are
+similar to lists except that instead of the values having integer
+indexes, dictionaries have keys or strings as indexes.
+
+Before we can proceed, start your IPython interpreter with the
+``-pylab`` option.
+
+{{{ start ipython interpreter by issuing command ipython -pylab }}}
+
+Let us start by creating an empty dictionary, type the following in
+your IPython interpreter.
+::
+
+    mt_dict = {}    
+
+Notice that unlike lists curly braces are used define ``dictionary``,
+
+{{{ move the mouse over curly braces to grab attention }}}
+
+Now let us see how to create a filled dictionary,
+::
+
+    extensions = {'jpg' : 'JPEG Image', 'py' : 'Python script', 'html' : 'Html document', 'pdf' : 'Portable Document Format'}
+
+Notice that each key-value pair is separated by a comma
+
+{{{ move the mouse over the commas to grab attention }}}
+
+and each key and value are separated using a colon.
+
+{{{ move the mouse over the colon one by one to grab attention }}}
+
+Here, we defined four entries in the dictionary extensions. The keys
+are
+
+{{{ spell the keys letter by letter }}}
+
+jpg, py, html, and pdf.
+
+Simply type,
+::
+
+    extensions
+
+in the interpreter to see the content of the dictionary. Notice that
+in dictionaries the order cannot be predicted and you can see that the
+values are not in the order that we entered in.
+
+Like in lists, the elements in a dictionary can be accessed using the
+index, here the index is the key. Try,
+::
+
+    print extensions['jpg']
+
+It printed JPEG Image. And now try,
+::
+
+    print extensions['zip']
+
+Well it gave us an error, saying that the key 'zip' is not in the
+dictionary.
+
+Pause here for some time and try few more keys. Also try jpg in
+capital letters.
+
+{{{ switch to next slide, adding and deleting keys and values in
+dictionaries }}}
+
+Well that was about creating dictionaries, now how do we add or delete
+items. We can add new items into dictionaries as,
+::
+
+    extensions['cpp'] = 'C++ code'
+
+and delete items using the ``del`` keyword as,
+::
+
+    del extension['pdf']
+
+Let us check the content of the dictionary now,
+::
+
+    extensions
+
+So the changes have been made. Now let us try one more thing,
+::
+
+    extensions['cpp'] = 'C++ source code'
+    extensions
+
+As you can see, it did not add a new thing nor gave an error, but it
+simply replaces the existing value with the new one.
+
+Now let us learn how to check if a particular key is present in the
+dictionary. For that we can use ``in``,
+::
+
+    'py' in extensions
+    'odt' in extensions
+
+So in short it will return ``True`` if the key is found in the
+dictionary, and will return ``False`` if key is not present. Note that
+we can check only for container-ship of keys in dictionaries and not
+values.
+
+{{{ switch to next slide, Retrieve keys and values }}}
+
+Now let us see how to retrieve the keys and values. We can use the
+method ``keys()`` for getting a list of the keys in a particular
+dictionary and the method ``values()`` for getting a list of
+values. Let us try them,
+::
+
+    extensions.keys()
+
+It returned the ``list`` of keys in the dictionary extensions. And now
+the other one,
+::
+
+    extensions.values()
+
+It returned the ``list`` of values in the dictionary.
+
+{{{ switch to next slide, problem statement for the next solved
+exercise }}}
+
+Now let us try to print the data in the dictionary. We can use ``for``
+loop to iterate.
+::
+
+    for each in extensions.keys():
+        print each, "-->", extensions[each]
+
+
+{{{ switch to next slide, recap }}}
+
+This brings us to the end of this tutorial, we learned dictionaries
+and saw how to create an empty dictionary, build a dictionary with
+some data in it, adding data, ``keys()`` and ``values()`` methods, and
+iterating over the dictionaries.
+
+{{{ switch to next slide, thank you slide }}}
+
+Thank you!
+
+..  Author: Anoop Jacob Thomas <anoop@fossee.in>
+    Reviewer 1:
+    Reviewer 2:
+    External reviewer: