* https://py-tutorial-de.readthedocs.io/de/python-3.3/introduction.html#zeichenketten-strings
  * http://www.tutorialspoint.com/python/python_strings.htm
  * http://www.python-kurs.eu/python3_sequentielle_datentypen.php
  * https://docs.python.org/3.5/reference/lexical_analysis.html#string-and-bytes-literals
  * https://docs.python.org/3.5/library/stdtypes.html#text-sequence-type-str
  * https://docs.python.org/3.5/library/string.html#format-examples
  * https://docs.python.org/3.5/tutorial/inputoutput.html#fancier-output-formatting