==========================
Data type: dictionary & if
==========================

.. _dictionary:

.. index:: Datatyp: dictionary, dictionary, if

.. |a| image:: /images/all/python-basics/curly_braces-100.png
   :width: 100px


Objectives
==========
   
.. tabularcolumns:: | c | l |
   :border: none

+-------+-------------------------------------------------------------------------+
|  |a|  | In other programming langauges a dictionary is named                    |
|       | »Associative array«, in Python it is named »Dictionary«.                |
|       | Some useful methods and scenarios are demonstrated.                     |
+-------+-------------------------------------------------------------------------+

Instructions
============
:Tasks:

1. Create a script: dictionaries.py 
2. Create a second version of the refrigerator example according to the station 
   for data type lists. 
3. Expand the mushroom example and generate a complete HTML page with *print* function. 

Properties of a dictionary
--------------------------

- Dictionaries are called mapping-type.
- They are similar to the associative array of other programming languages.
- They are represented by a pair of curly brackets *{}* and always contain
  name/value pairs that are separated by a colon. Names are also called *keys*
- The order of the key values ​​in the dictionary is random.

Examples
========
::

  cars = {'BMW':'Germany', 'Renault':'France', 'Volvo':'Sweden'}
  
  # other stucture...
  
  cars = {'BMW':'Germany', 
          'Renault':'France', 
          'Volvo':'Sweden'}

.. list-table::
   :widths: 20 20 40
   :header-rows: 1

   * - Method
     - Note
     - Example, comment

   * - clear()
     - removes all entries from a dictionary
     - cars.clear()

       the result os an empty dictionary {}
   * - copy()
     - copy all entries af a give dictionary
     - copy_of_cars = cars.copy()

   * - has_key()
     - returns the value 1 if the key exists if not 0
     - cars.has_key('Volvo')

   * - items() 
     - returns all name/value pairs each as a tuple
     - cars.items()

   * - keys()
     - returns a list of all keys
     - cars.keys()                 |
   * - update()
     - add a new name/value, if the key exists the value will be replaced
     - cars['Skoda'] = 'Czech Republic'

   * - get()
     - return the value to a give name
     - cars.get('Volvo')

       cars.get('xyz','???') 

Second Example
--------------
:: 
  
  # create a dictionary...
 
  mushrooms = {} # empty dictionary
  mushrooms['cep'] = ['eatable x times', "mixed forest", "Boletus edulis"]
  mushrooms['fly amanita'] = ["eatable once", "coniferous forest", "Amanita muscaria"]
  mushrooms['bay bolete'] = ["eatable x times", "mixed forest", "Boletus badius"]
  mushrooms['Coprinus'] = ['eatable x times', "meadow", "Coprinus"]

  # print the content:

  print('''Pretty print dictionary of mushrooms:\n ''')

  for i in mushrooms.keys():
      print("""kind = {}, eatable = {}, be found = {}; """.format(i, 
                                                                  mushrooms[i][0],
                                                                  mushrooms[i][1]))

In this example some other data types are used or created.

- Dictionary = mushrooms
- List = as result of the mehtod call keys()
- Tupel = as parameter of the format method

Many more variations are possible eg. combined with a  :ref:`Slicing <slicing>` -operator.