Add IFS in python (#700)

Author: jonathanvanschenck

CONTRIBUTORS.md

@@ -42,10 +42,11 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - Christopher Milan
 - Vexatos
 - Raven-Blue Dragon
-- Björn Heinrichs 
+- Björn Heinrichs
 - Olav Sundfør
 - Ben Chislett
 - dovisutu
 - Antetokounpo
 - Akash Dhiman
 - Vincent Zalzal
+- Jonathan D B Van Schenck

contents/IFS/IFS.md

@@ -130,6 +130,8 @@ Here, instead of tracking children of children, we track a single individual tha
 [import:4-17, lang:"julia"](code/julia/IFS.jl)
 {% sample lang="cpp" %}
 [import:39-52, lang:"cpp"](code/c++/IFS.cpp)
+{% sample lang="py" %}
+[import:5-12, lang:"python"](code/python/IFS.py)
 {% endmethod %}
 
 If we set the initial points to the on the equilateral triangle we saw before, we can see the Sierpinski triangle again after a few thousand iterations, as shown below:
@@ -195,6 +197,8 @@ In addition, we have written the chaos game code to take in a set of points so t
 [import, lang:"julia"](code/julia/IFS.jl)
 {% sample lang="cpp" %}
 [import, lang:"cpp"](code/c++/IFS.cpp)
+{% sample lang="py" %}
+[import, lang:"python"](code/python/IFS.py)
 {% endmethod %}
 
 ### Bibliography

contents/IFS/code/python/IFS.py

@@ -0,0 +1,25 @@
+from random import random, choice
+from math import sqrt
+
+# This generator simulates a "chaos game"
+def chaos_game(n, shape_points):
+    # Initialize the starting point
+    point = [random(), random()]
+
+    for _ in range(n):
+        # Update the point position and yield the result
+        point = [(p + s) / 2 for p, s in zip(point, choice(shape_points))]
+        yield point
+
+# This will generate a Sierpinski triangle with a chaos game of n points for an
+# initial triangle with three points on the vertices of an equilateral triangle:
+#     A = (0.0, 0.0)
+#     B = (0.5, sqrt(0.75))
+#     C = (1.0, 0.0)
+# It will output the file sierpinski.dat, which can be plotted after
+shape_points = [[0.0, 0.0],
+                [0.5, sqrt(0.75)],
+                [1.0, 0.0]]
+with open("sierpinski.dat", "w") as f:
+    for point in chaos_game(10000, shape_points):
+        f.write("{0}\t{1}\n".format(*point))