=======
Slicing 
=======

.. index:: slicing

.. _slicing:

.. |a| image:: /images/all/python-basics/slicing-operator-100.png


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

+-------+-------------------------------------------------------------------------+
|  |a|  | *Slicing* is a useful technique to operate on all sequenz data types.   |
|       | Helpful examples are given in this station.                             |
+-------+-------------------------------------------------------------------------+

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

1. Create a tuple or a list with the following sentence and store each word as a 
   value: "Simple is better than complex"
2. Return the last value of the tuple or list.
3. Create a dictionary with ten concept pairs <first language> -- <second language>.
4. Print the content of the dictionare in order.
5. Construct a data structure which stores the position of a chess game.
6. Return the position as ASCII art.

What is slicing?
================
It is the selection of a subset of a sequence of values.
This works with strings, tuples and lists alike.

Cut part range from - to:
::

  s = "Big Bug Bunny"
  part = s[8:10]
  print(s, part)

Cut the last part:
::

  s = "Big Bug Bunny"
  part = s[-1:]
  print(s, part)

Cut first element:
::

  s = "Big Bug Bunny"
  part = s[0]
  print(s, part)

Cut all elements:
::

  s = "Big Bug Bunny"
  part = s[:] # same as s without braces
  print(s, part)

Nested Views
============

What applies to the strings, can also be applied to :ref:`tuples <tuple>` and :ref:`lists <lists>`.
If the element is a character string, it can also partly cut again:

.. ifconfig:: language=='de'

   ::

     t1 = ('Das', 'tapfere', 'Schneiderlein', 'traf', 7, 'auf', 'einen', 'Streich')
     t2 = t1[2][3:7]
     print(t2)

.. ifconfig:: language=='en'

   ::
       
     t1 = ('The', 'quick', 'brown fox', 'jumps', 'over', 'the', 'lazy', 'dog')
     t2 = t1[2][3:8]
     print(t2)


Dictionaries and slicing
========================
For the data type * dictionary * there is no slicing operator! 
Various methods returns a list as a result. If the result is a list, 
slicing is possible again.

:: 
  
  # 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]))