add classes for constraints

Constraint.py

@@ -0,0 +1,3 @@
+
+class Constraint(object):
+    pass

DistanceConstraint.py

@@ -0,0 +1,10 @@
+
+from Constraint import Constraint
+
+class DistanceConstraint(Constraint):
+    def __init__(self, shape1, attr1, shape2, attr2, dist):
+        self.shape1 = shape1
+        self.shape2 = shape2
+        self.attr1 = attr1
+        self.attr2 = attr2
+        self.dist = dist

EqualConstraint.py

@@ -0,0 +1,9 @@
+
+from Constraint import Constraint
+
+class EqualConstraint(Constraint):
+    def __init__(self, shape1, attr1, shape2, attr2):
+        self.shape1 = shape1
+        self.shape2 = shape2
+        self.attr1 = attr1
+        self.attr2 = attr2

Sketch.py

@@ -2,6 +2,7 @@
 class Sketch(object):
     def __init__(self):
         self.shapes = []
+        self.constraints = []
 
     def __iter__(self):
         return self.shapes.__iter__()