=================
Data type: string
=================

.. _strings:

.. index:: string, data type: string

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

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

+-------+-------------------------------------------------------------------------+
|  |a|  | Every programming language is using strings as a data type.             |
|       | The Python way to handle strings, is shown in this station.             |  
+-------+-------------------------------------------------------------------------+

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

1. Save the following text, line by line into variables:

.. ifconfig:: language == 'en'

   ::
     
      "Shall I compare thee to a summer's day?
      Thou art more lovely and more temperate..." 
   
      Lines from Shakespeare's Sonnet 18.

.. ifconfig:: language == 'de'

   ::

      "Soll ich dich einem Sommertag vergleichen?
      Er ist wie du so lieblich nicht und lind;..."

      Zeilen aus dem Sonnet 18 von Shakespeare

2. Return the values of all variables with the print-Function. 
   Don't forget the empty line. 


Properties and rules 
====================

- A string is enclosed in the following characters: single quotation, double quotation and triples of the quotation signs.
- Strings are immutable, if you change a string, the computer has to reserve new memory and afterward release the old memory.
- Each character is callable with an index. The index counting starts at zero.

More hints about strings kann be found at:

.. ifconfig:: language == 'en'

   `Wikipedia: String (computer science) <http://en.wikipedia.org/wiki/String_%28computer_science%29>`_
 
.. ifconfig:: language == 'de'

   `Wikipedia: Zeichenketten <http://de.wikipedia.org/wiki/Zeichenkette>`_

Assign strings
==============
Each variable get's own value.

.. ifconfig:: language == 'en'
   
   todo: find a good equivalent to the german version...

.. ifconfig:: language == 'de'

   ::

      a = "Fliegen "
      b = 'fliegen!'
      c = ''          # an empty string

      print(a, b, c)


Concatenate strings
-------------------
Building longer Strings from substrings, is an often used technique.

.. ifconfig:: language == 'de'

   ::

     a = "Fliegen"
     b = "fliegen"
     c = "Wenn " + a + " hinter " + a + " " + b + ",\n"
     c = c + "dann " + b + " " + a + " " + a + " hinterher!"
     print(c)

:Hint: The same result can be achieved with other data types :ref:`tuple <tuples>` and :ref:`list <lists>`.

Extract parts of string
-----------------------
This task is possible with the slicing operator. This operation is available for all sequence data types. See also :ref:`slicing <slicing>`.


Wildcards and strings
---------------------
It is also posseble to include strings in an other string with predefined slots. The percent character(%) is used as a place-marker, followed by a single character s (%s). More about this techniques can be found in the learning station :ref:`modulo <formating>`.