# Intro to Python Scripting: 24 Recursion Cracking

Software:
Tag:
Video Duration:
13 minutes
Author:
Zach Downey

In this tutorial we create a cracking algorithm using recursion in python. This tutorial is inspired by the Aranda/Lasch Pamphlet Architecture 27 : Tooling. It's an awesome book, I highly reccommend. Anyway, we start with a polygon and find it's area centroid. We then explode the polygon and extract each of the line segements. For each line segment we get the start and endpoints of the line and create a new polygon from those points and the centroid. We then add all of those new polygons to the polygon list and repeat until the count gets to zero.

```#cracking algorithm
import rhinoscriptsyntax as rs
import Rhino
import scriptcontext

def crackpolygon(pls, count):
temppls = pls
pls = []
if count == 0:
return 1
else:
for pl in temppls:
if rs.CloseCurve(pl) == False:
print "Not a closed curve"
else:
#print "Cool"
centroid = rs.CurveAreaCentroid(pl)
curves = rs.ExplodeCurves(pl)
for crv in curves:
#print crv
pt1 = rs.CurveStartPoint(crv)
pt2 = rs.CurveEndPoint(crv)
pts = []
pts.append(pt1)
pts.append(pt2)
pts.append(centpt)
pts.append(pt1)
pls.append(newpl)
rs.DeleteObject(crv)
cleanup = []
cleanup.append(centpt)
#cleanup.append(curves)
rs.DeleteObjects(cleanup)
count = count - 1
return crackpolygon(pls, count)

count = rs.GetInteger("How many iterations would you like to do?", 3)
pl = rs.GetCurveObject("pick a closed curve to crack")
plguid = pl
polygons = []
polygons.append(plguid)
crackpolygon(polygons, count)```

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