Sphinx build

Author: foonicorn

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+# Sphinx build info version 1
+# This file hashes the configuration used when building these files. When it is not found, a full rebuild will be done.
+config: 5ce55d88e65e0217306dc230d617f309
+tags: fbb0d17656682115ca4d033fb2f83ba1

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+User-defined funtions
+*********************
+
+Introduction
+============
+
+There is still a lot of duplicated code --- the actual drawing of the rectangle
+--- around. If you need to copy and paste code, that is usually a sign of
+lacking abstractions. (Programmers call it a *code smell.*)
+
+Functions are one way to express abstractions in Python. Let's take
+``reset()`` for example. It is actually an abstraction for a number of steps,
+namely:
+
+* Erase the drawing board
+* Set the width and color back to default
+* Move the turtle back to its initial position
+
+A function can be defined with the ``def`` keyword in Python::
+
+    def line_without_moving():
+        forward(50)
+        backward(50)
+
+You can access names in functions as well::
+
+    size = 50
+    def line_without_moving():
+        forward(size)
+        backward(size)
+
+A function for a square
+=======================
+
+Exercise
+--------
+
+Write a function that draws a square. Can you see how you could improve the
+tilted squares program with that and greatly relieve experimentation?
+
+
+A function for a hexagon
+========================
+
+Exercise
+--------
+
+Write a function that draws a hexagon.
+
+.. image:: /images/hexagon.png
+
+Now combine that function into a honeycomb.
+
+.. image:: /images/honeycomb.png
+
+Solution
+--------
+
+::
+
+    def hexagon():
+        forward(100)
+        left(60)
+        forward(100)
+        left(60)
+        forward(100)
+        left(60)
+        forward(100)
+        left(60)
+        forward(100)
+        left(60)
+        forward(100)
+        left(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+
+    hexagon()
+    forward(100)
+    right(60)
+

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+Functions with parameters
+*************************
+
+Todo

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+Introduction to Programming with Python
+***************************************
+
+
+Table of contents:
+
+.. toctree::
+    :maxdepth: 2
+   
+    interactive_work
+    simple_drawing
+    names
+    functions
+    loops
+    functions_parameters
+

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+Interactive work
+****************
+
+Todo

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+Loops
+*****
+
+Introduction
+============
+
+One more thing: Our programs often featured repetition. There is a powerful
+concept in Python called looping, which we will elaborate later on. For now,
+take that easy example::
+
+    for i in range(10):
+        print "Hello!"
+
+Drawing a dashed line
+=====================
+
+Exercise
+--------
+
+Draw a dashed line.  You can move the turtle without tracing a line behind you
+with the ``up()`` function;  put it back on the ground with ``down()``.
+
+.. image:: /images/dashed.png
+
+Solution
+
+::
+
+    for i in range(10):
+        forward(15)
+        up()
+        forward(5)
+        down()
+
+Bonus
+-----
+
+Can you make the dashes become larger as the line progresses?
+
+.. image:: /images/dashedprogressing.png
+
+Honeycomb loops
+===============
+
+Exercise
+--------
+
+Take your honeycomb program and make it easier with loops.  How small can you
+get it?
+
+Solution
+--------
+
+::
+
+    def hexagon():
+        for i in range(6):
+            forward(100)
+            left(60)
+
+    for i in range(6):
+      hexagon()
+      forward(100)
+      right(60)

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+Names
+*****
+
+Introduction
+============
+
+Whew. Experimenting with the angles requires you to change three different
+places each time. Imagine you'd want to experiment with the square sizes, let
+alone with rectangles! We can do better than that.
+
+This is where names come into play: You can tell Python that from now on,
+whenever you refer to a name, you actually mean something else. That concept
+might be familiar from symbolic maths, where you would write: *Let x be 5.*
+Then x*2 will obviously be 10. That's why those names are known as variables,
+too.
+
+In Python syntax, that very statement translates to::
+
+    x = 5
+
+After that statement, if you do ``print x``, it will actually output its value
+--- 5.  You can well use that for turtle too::
+
+    forward(x)
+
+A variable called angle
+=======================
+
+Exercise
+--------
+
+If we have a variable called ``angle``, how could we use that to experiment
+much faster with our tilted squares program?
+
+Solution
+--------
+
+::
+
+    from turtle import *
+    angle = 20
+
+    left(angle)
+
+    forward(50)
+    left(90)
+    forward(50)
+    left(90)
+    forward(50)
+    left(90)
+    forward(50)
+    left(90)
+
+    left(angle)
+    # ...
+
+Bonus
+-----
+
+Can you apply that principle to the size of the squares, too?
+
+The house of santa claus
+========================
+
+Exercise
+--------
+
+Draw a house.
+
+.. image:: /images/house.png
+
+You can calculate the length of the diagonal line with Pythagoras. That value
+is a good candidate for a name binding.
+
+